ArticlePDF Available

Presumptions in Legal Argumentation

October 2012
Ratio Juris 25(3):271-300

DOI:10.1111/j.1467-9337.2012.00514.x

Authors:

Fabrizio Macagno

University of Lisbon

Douglas Walton

University of Windsor

In this paper a theoretical definition that helps to explain how the logical structure of legal presumptions is constructed by applying the Carneades model of argumentation developed in artificial intelligence. Using this model, it is shown how presumptions work as devices used in evidentiary reasoning in law in the event of a lack of evidence to assist a chain of reasoning to move forward to prove or disprove a claim. It is shown how presumptions work as practical devices that may be useful in cases in which there is insufficient evidence to prove the claim to an appropriate standard of proof.

The function of a presumption in a mass of evidence in a typical case.

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Evidential situation before a presumption has been accepted.

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Evidential situation after the presumption has been accepted.

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Strengths of Presumptions

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Epistemic foundations of presumptions and their effects

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Presumptions

in Legal Argumentationraju_514 271..300

FABRIZIO MACAGNO* AND DOUGLAS WALTON**

Abstract. In this paper a theoretical deﬁnition that helps to explain how the logical

structure of legal presumptions is constructed by applying the Carneades model of

argumentation developed in artiﬁcial intelligence. Using this model, it is shown

how presumptions work as devices used in evidentiary reasoning in law in the

event of a lack of evidence to assist a chain of reasoning to move forward to prove

or disprove a claim. It is shown how presumptions work as practical devices that

may be useful in cases in which there is insufficient evidence to prove the claim to

an appropriate standard of proof.

Recent work in the interdisciplinary area between artiﬁcial intelligence and

law has advanced logical models of presumption and the burden of proof

using an argumentation approach (Gordon and Walton 2009; Prakken and

Sartor 2009). However, presumption and its companion notion of burden

of proof have been said to be two of the slipperiest concepts in law (Strong

1992, 449). After surveying the various notions of presumption in the law

of evidence, and showing how disparate they are, Allen (1981, 865)

commented, “the ambiguity and confusion surrounding presumptions

continued unabated.” However, Allen (1980) has argued that presumption

can be understood in law as a device for shifting the burden of persuasion

in a trial setting. This view represents the approach we take in this paper,

basing our analysis on the theory that, in addition to the burden of

persuasion and the burden of producing evidence, there is a third kind of

burden in legal reasoning, called the tactical burden of proof (Prakken and

* Fabrizio Macagno would like to thank the Fundação para a Ciência ea Tecnologia for the

research grant on Argumentation, Communication and Context (PTDC/FIL-FIL/110117/2009)

and the international law ﬁrm Martinez & Novebaci for providing materials and consultancy

that proved to be extremely helpful for the research in this paper.

** Douglas Walton would like to thank the Social Sciences and Humanities Research Council

of Canada for a research grant that supported the work in this paper.

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Ratio Juris. Vol. 25 No. 3 September 2012 (271–300)

Street, Malden 02148, USA.

Sartor, 2009). Both in law and in the argumentation literature generally, it

is often said that a presumption is a device that shifts the burden of proof

back and forth from one party to the other in a dialogue. Recent work in

artiﬁcial intelligence and law has produced precise models of burden of

proof that not only draw the traditional distinction between two kinds of

burden of proof, the burden of persuasion and the burden of producing

evidence (burden of production), but also introduce a third type of burden

called the tactical burden of proof.

In the theory outlined in this paper, a presumption in evidential rea-

soning is an assumption that a fact obtains, an assumption that can be

made without proof in some situations. Thus it will be shown by examples

that a characteristic of presumption is that it is a proposition accepted as

factual in law, even though it has not been proved. This characteristic links

it to another one: a presumption is a statement that is accepted in law even

though it does not meet the burden of proof that would normally be

required for the statement to be acceptable to a standard of proof appro-

priate in a framework of legal evidence. It will be shown how presump-

tions are useful in situations where there is a lack of evidence.

Much recent work in artiﬁcial intelligence and law, and in the related

ﬁeld of argumentation studies generally, has now adopted a dialogical

model of argumentation. In this paper we show how this dialogical model

can be used to draw a much clearer distinction than was possible in the

past between presumption and related notions in legal argumentation. We

see our paper as a contribution to the new evidence scholarship, an

interdisciplinary ﬁeld of research that uses formal models of reasoning and

computational tools for representing legal argumentation to move forward

with the intention of supporting Wigmore’s claim that there is a science of

proof underlying the law of evidence (Park and Saks 2006). We begin with

an outline of recent work on the burden of proof in artiﬁcial intelligence

and law that brieﬂy shows how this approach is based on an argumenta-

tion model. In this model an argument is seen not only as an inference

from premises to a conclusion, but also as presupposing a context of

dialogue in which two or more parties take turns, making moves in the

form of speech acts.

1. The Dialogical Framework

Prakken and Sartor (2009, 228) have built a logical model of the burden of

proof in law. The burden of persuasion speciﬁes which party has to prove

an ultimate probandum in the case, and also the standard of proof that has

to be met. The burden of production speciﬁes which party has to offer

evidence on some speciﬁc issue at some stage during the argumentation in

the trial. Both the burden of persuasion and the burden of production are

assigned by law, whereas the tactical burden of proof is decided by the

272 Fabrizio Macagno and Douglas Walton

party putting forward an argument during a move. The judge is supposed

to instruct the jury on the standard of proof to be met at the beginning of

the trial. The burden of production may in many instances only have to

meet a low standard of proof. If the evidence produced does not meet the

standard, the issue can be decided as a matter of law against the relevant

party, or decided in the ﬁnal stage by the judge. Both the burden of

persuasion and the burden of production are assigned by law. The tactical

burden of proof, on the other hand, is decided by the party putting

forward an argument at some stage during the proceedings. The arguer

must judge the risk of ultimately losing on the particular issue under

discussion at that point if he or she fails to put forward further evidence

concerning that issue.

The relationship between the burden of persuasion and the burden of

production works differently in criminal and civil cases (Prakken and

Sartor 2009, 225–6). In civil cases the general rule is that the burden of

persuasion is on the party making the claim, as well as the burden of

production for any claim made, while both burdens are on the other

party for an exception. For example, in the case of a dispute over a

contract, the party claiming that a contract exists has to prove that there

was an offer that was accepted. These are the two elements of proving

a contract. However, there can be exceptions to this rule: for example,

one party might claim that the other party deceived him. In such a case,

both the burden of production and the burden of persuasion that there

is a contract are on the party making the claim, but then the burden of

production shifts to the party claiming an exception. In criminal cases,

on the other hand, the burden of production and the burden of persua-

sion may be on different parties. In criminal cases, the prosecution has

to meet the beyond reasonable doubt standard to prove that the defen-

dant is guilty. This principle also covers the nonexistence of exceptions.

No weakness in its argument can be left by the prosecution, or proof

beyond reasonable doubt will not be established.

For example, in a murder case, the burden of persuasion is on the

prosecution not only to prove the two elements that there was a killing

and that it was done with intent, but also to prove the nonexistence of

an exception, such as the claim that the killing was in self-defense.

However, the burden of production for proving an exception is on the

defense. For example, a defendant who has pleaded self-defense will

have to produce evidence to support this claim. Once this burden of

production has been met, even by means of a small amount of evidence,

not large enough to meet the requirements of the beyond reasonable

doubt standard, the burden of persuasion that there was no self-defense

is then on the prosecution. It is in this kind of case that the language of

shifting the burden of proof is often used to describe the logical mecha-

nism of what has happened.

273Presumptions in Legal Argumentation

According to Prakken and Sartor (2009, 227), the distinction between the

burden of production and tactical burden of proof is usually not clearly

made in common law, nor explicitly considered in civil law countries.

However, they add that the distinction is relevant for both systems of law,

because it is induced by the logic of the reasoning process. Certainly it is not

easy at ﬁrst to clearly grasp the distinction between the burden of production

and the tactical burden of proof, but from the point of view of understanding

the burden of proof as a concept of logical reasoning, both in law and in

everyday conversational argumentation, it is important to attempt to do so.

The distinction can be clariﬁed by going back to the example of a murder

trial in which the prosecution has provided evidence to establish killing and

intent, and the defense has produced evidence in favor of a plea of

self-defense. In such a case, if the prosecution does not rebut the claim of

self-defense by putting forward a counterargument, they stand a good

chance of losing the case. In such an event, we can say that not only is the

burden of persuasion on the prosecution, but also the tactical burden of

proof with respect to the plea of self-defense (Prakken and Sartor 2009, 227).

What is especially interesting is the observation that such a tactical burden

can shift back and forth between the parties any number of times during the

trial, depending on “who would be likely to win if no more evidence were

provided” (Prakken and Sartor 2009, 227). To revert to the example, suppose

that the prosecution has now produced evidence that goes against the

previous argument for self-defense, and the defendant has not rebutted that

argument. It is now the defendant who stands to lose. The tactical burden of

proof, it can be said, has now shifted to the defendant. However, it is

important to note that according to Prakken and Sartor (2009, 227) the

burden of production never shifts. Once it has been fulﬁlled, it is disregarded

for the rest of the trial. In their view, the tactical burden is the only one of the

three burdens that can properly be said to shift.

The Carneades Argumentation System is an extremely useful instrument

for analyzing the burden of proof. This is a mathematical model consisting

of deﬁnitions of mathematical structures and functions based on these

structures (Gordon, Prakken and Walton 2007). It is also a computational

model, meaning that all the functions of the model are computable. It

deﬁnes the mathematical properties of arguments that are used to identify,

analyze and visualize real arguments. Carneades models the structure and

applicability of arguments, the acceptability of statements, and proof

standards. It has been implemented using a functional programming

language, adopting a graphical user interface.1Carneades models argu-

mentation as a dialogue in which two parties (in the simplest case) take

turns to perform moves in the form of speech acts, such as asking a

question or putting forward an argument (Table 1).

1http://carneades.github.com

274 Fabrizio Macagno and Douglas Walton

A dialogue is formally deﬁned as an ordered 3-tuple 〈O, A, C〉where O

is the opening stage, Ais the argumentation stage, and Cis the closing

stage (Gordon and Walton 2009, 5). Dialogue rules (protocols) deﬁne what

types of speech acts are allowed in moves by the parties during the

argumentation stage (Walton and Krabbe 1995). The initial situation is

framed at the opening stage, and the dialogue moves through the opening

stage toward the closing stage. The burden of persuasion is established at

the opening stage of a dialogue, while burdens of production and tactical

burdens are brought into play at the argumentation stage. The shifting

back and forth of the tactical burden during the argumentation stage has

an effect on whether the burden of persuasion speciﬁed at the opening

stage is met or not. This effect is calculated and summed up at the closing

stage, determining which side has won the case by producing evidence

sufficient to meet the standard of proof that has been set for it.

Carneades uses this dialogue structure to model standards of proof that

can be met by arguments. For an argument to meet the scintilla of evidence

(SE) standard, there must be at least one applicable argument2for a claim

made. For an argument to meet the preponderance of evidence (PE)

standard, SE should be satisﬁed and the maximum weight assigned to an

applicable pro argument (for the claim) needs to be greater than the

maximum weight of an applicable con argument (against the claim). For an

argument to meet the clear and convincing evidence standard (CCE), PE

should be satisﬁed, the maximum weight of applicable pro arguments

should exceed some threshold a, and the difference between the maximum

weight of the applicable pro arguments and the maximum weight of the

applicable con arguments should exceed some threshold b. Finally, for an

argument to meet the beyond reasonable doubt (BRD) standard, CCE must

be satisﬁed and the maximum weight of the applicable con arguments

must be less than some threshold g. The thresholds a,band gare left open,

and not given ﬁxed numerical values.

2An argument is considered to be applicable if its premises are not defeated and there is no

exception to the inference.

Table 1 Some Types of Speech Act in a Dialogical Format

Speech act Dialogue form Function

Question (yes-no type) S? Speaker asks whether S is the case.

Assertion (claim) Assert S Speaker asserts that S is the case.

Concession (acceptance) Accept S Speaker incurs commitment to S.

Retraction (withdrawal) No commitment S Speaker removes commitment to S.

Challenge (demand for

proof of claim)

Why S? Speaker requests that hearer give an

argument to support S.

Put Argument Forward P1,P

2,...,P

ntherefore S. P1,P

2,...,P

nis a set of premises that

give a reason to support S.

275Presumptions in Legal Argumentation

It is highly questionable whether a precise deﬁnition of the beyond

reasonable doubt standard suitable for use in the courts can be given. Courts

have often held that the legal concept of reasonable doubt cannot be deﬁned

precisely, for example by citing numerical probability values (Tillers and

Gottfried 2006). However, presumptions have been analyzed in argumen-

tation theory considering their dialogical function of shifting the burden of

proof (Pinto 1984; Walton 1993, 2008b). Thus, by formulating standards of

proof in a dialogue model of argumentation like Carneades, part of the work

is done to gain a better understanding of how presumptions work by

shifting the burden of proof in dialectical settings. It is precisely this sort of

dialectical model that can be used to analyze how presumption functions in

reasoned argumentation.

2. The Two Dimensions of Presumption: Defeasible

Inference Structures

Godden and Walton (2007) summarized several different theories of pre-

sumption in argumentation studies from Whately onwards. However, the

approach taken in this paper deﬁnes presumption in terms of an inference

with three components (Ullmann-Margalit 1983, 147): (1) the presumption-

raising fact in a particular case at issue, (2) the presumption formula, i.e.,

a defeasible rule that sanctions the passage from the presumed fact to the

conclusion, (3) the conclusion, a proposition that is presumed to be true on

the basis of (1) and (2). Rescher (2006, 33) helpfully outlined the structure

of this type of inference as follows.

Premise 1: P(the proposition representing the presumption) obtains

whenever the condition Cobtains unless and until the standard default

proviso D(to the effect that countervailing evidence is at hand) obtains

(Rule).

Premise 2: Condition Cobtains (Fact).

Premise 3: Proviso Ddoes not obtain (Exception).

Conclusion: Pobtains.

This analysis is on the right track, in our view, because it deﬁnes a

presumption using a defeasible rule. The problem is that it does not go far

enough to enable us to tell what the difference is between a defeasible rule

and a presumption. In our view a presumption is a special type of

defeasible rule. In contrast, the Prakken-Sartor (2006) model represents

presumption as equated with the rule that is part of a defeasible inference,

and that takes the form of a defeasible generalization. As an example, they

use a case where the plaintiff demands compensation on the ground that

the defendant damaged his bicycle. The burdens of production and per-

suasion that the bicycle was damaged and that he owned it are on the

276 Fabrizio Macagno and Douglas Walton

plaintiff. One way he can prove that he owns the bicycle is to demonstrate

that he possesses it. According to Dutch law in such a case, given

possession, ownership of the bicycle can be presumed. The presumption in

such a case can be expressed by the proposition that possession of an object

can be taken as grounds for concluding that the person who possesses the

object owns it. According to the Prakken-Sartor theory, this proposition has

the form of a defeasible rule, and generally speaking, any legal presump-

tion can be cast in the form of such a defeasible rule. The defeasible rule

is this proposition: normally if a person possesses something, it can be

taken for granted that he owns it, unless there is evidence to the contrary.

It is held to be a defeasible rule in the Prakken-Sartor theory in the same

way as the following proposition: if Tweety is a bird, then normally, but

subject to exceptions, Tweety can ﬂy. Such a proposition is a defeasible rule

in that it holds generally, but can default in the case of an exception, for

example in the case that Tweety is a penguin. The argument map shown

in Figure 1 can be used to give the reader an initial idea of how presump-

tion works as an argumentation device in the Carneades model. In

Figure 1, the text boxes are nodes of the graph that represent propositions

(statements) that can be premises or conclusions in a chain of argumen-

tation. The ultimate proposition to be proved in a case is displayed on the

left. It is called the ultimate probandum. The lines and arrows represent

arguments from premises to a conclusion. Arguments are represented by

the circles shown in Figure 1. An argument can be pro or contra with

respect to the conclusion that the premises are supposed to support. All

three arguments shown in Figure 1 are pro arguments, that is, they are

arguments that present evidence that supports the conclusion. Figure 1 is

intended to represent the typical kind of case in which the bringing

forward of a presumption is part of a chain of argumentation representing

a body of evidence supporting or attacking a designated conclusion.

In the situation in Figure 1, there is insufficient evidence to prove the

claim. This implies that there is some evidence, and that this evidence is

insufficient to prove the claim that is the ultimate probandum in the case. It

is shown in the middle of Figure 1 that the reason why there is a lack of

sufficient evidence to prove the conclusion is that the argument fails to

meet its required standard of proof. The role of a presumption in such a

Figure 1: The function of a presumption in a mass of evidence in a typical case.

277Presumptions in Legal Argumentation

case is to act as an additional premise in the argument (in some instances

it could be a separate argument) that can overcome this lack of evidence,

by appeal to a legal rule that functions as a generalization that can be

combined with a fact in the case to make an inference. What this shows is

that a presumption is made up from premises of a fact and a legal rule that

join together in a defeasible inference to generate a conclusion that can ﬁll

a gap in an argument caused by lack of sufficient evidence to meet a

standard of proof.

3. Presumptions in a Dialectical Perspective

Presumptions can be distinguished from assumptions or ordinary state-

ments because the respondent in a dialogue cannot simply reject them; in

order not to make a commitment to a presumption, the interlocutor needs to

provide a rebuttal (Walton 1993, 139–40). If we consider presumption from

a dialectical point of view, we can notice that the dialectical move of

presumption consists of three essential elements. (1) It must be based on a

generally accepted principle of inference (otherwise it would be an assump-

tion). (2) It is used in conditions of lack of evidence to meet a standard of

proof (otherwise it would be an ordinary defeasible inference of any kind).

(3) It is used to shift a burden of proof in types of dialogue characterized by

an opposition of viewpoints and argumentation, such as persuasion dia-

logue (Walton 2010).3The rationale behind this kind of deﬁnition of the

notion of a presumption was shown in Figure 1 using the graphical interface

of the Carneades system. In this model, in order to establish a judicial proof

of a claim, there has to be an assumption that enough evidence has been

collected so that this conclusion can be established for meeting an appro-

priate standard of proof. The four standards of proof used in Carneades’

deﬁnition (Gordon and Walton 2009) can be used to give the reader an idea

of how appropriate proof standards can be set in an orderly procedure of

argumentation in a model of evidential reasoning.

Figure 2 shows the paradigm case in which a presumption is brought

forward within a mass of evidence that has been presented to support a

claim to be proved on one side of the case. In the Carneades graphical user

interface, when a proposition appears in the shaded text box with a

checkmark in front of the proposition, it means that this proposition has

been accepted. When a proposition appears in the text box where the

background is white, and a question mark appears in front of the propo-

sition, it means that the proposition is questionable. To say it has been

stated means that it has not been accepted. The shaded boxes in the middle

column show the three elements that make bringing forward a presump-

3It is used in a different way in deliberation dialogue (McBurney et al. 2007) where the aim

is to decide what to do in a situation with changing circumstances.

278 Fabrizio Macagno and Douglas Walton

tion a useful move. First, there is some evidence to prove the claim; second,

there is lack of sufficient evidence to prove the claim; third, there is no

evidence to disprove the claim.

If we look at all the shaded boxes in Figure 2, we can see that the

evidence is insufficient to prove the claim on the left of the ﬁgure.

However, let us say that in this situation, a presumption could be brought

forward that would ﬁll the evidential gap. This kind of situation is shown

in Figure 3.

The transition between the evidential situation represented in Figure 2

and that represented in Figure 3 shows how Carneades works as a model

that can be used to represent argument evaluation. As shown in Figure 3,

once the law stating the presumption has been brought in and joined to an

appropriate fact in the case (not shown in the diagram), the presumption

is accepted. Once the presumption is shown as accepted, provided the

presumption along with the other arguments in the case is sufficient to

prove the claim shown on the far left, Carneades automatically shows the

claim to be proved as accepted. In other words, Carneades displays the

claim to be proven with a checkmark in front of it in a shaded box. When

the system is used on a computer, it shows all such boxes colored in green,

to contrast them with the text boxes that are shown with no color.

Figure 2: Evidential situation before a presumption has been accepted.

Figure 3: Evidential situation after the presumption has been accepted.

279Presumptions in Legal Argumentation

The dialectical effects of presumption can therefore be modeled by using

computing systems that can describe the possible dialectical scenarios.

However, the analysis of presumptions needs to take argument evaluation

into consideration. As seen above, presumptions are rebuttable. But how?

Why do they shift the burden of proof? Why do they operate only in the case

of a lack of evidence? To answer these questions we need to take a step

further and analyse their inferential structure and dialectical foundation.

4. Structure of Presumptions: Dialectical Effects and

Epistemic Foundation

Presumptions, as mentioned above, can be described considering their

inferential structure, their dialogical effect, and their epistemic foundation.

The three elements are strictly connected, and will be shown to determine

each other.

4.1. The Rational Principle

The ﬁrst essential element is that the conclusion, or the presumption, needs

to be supported by a rational principle (Ullmann-Margalit 1983, 147), that

“may be grounded on general experience, or probability of any kind; or

merely on policy and convenience” (Thayer 1898, 314). Nowadays pre-

sumptions in law are distinguished in three categories: 1. presumptions of

fact, or presumptio hominis (conclusions drawn from principles from every-

day experience and past facts, see Berger 1953, 646), 2. presumptions of law

(inferences grounded on legal rules), and 3. irrebuttable presumptions, or

praesumptio iuris et de iure (conclusions from principles of law that cannot

be refuted) (see Park, Leonard and Goldberg 1998). The difference between

the three types of presumption can be explained by the following rules of

inference:

1. Things once proved to have existed in a particular state continue to

exist in that state (Reynolds 1897, 118);

2. A person not heard from in ﬁve years is presumed to be dead

(California Evidence Code, section 667; 663);

3. No child under the age of 10 can be guilty of an offence. (Children and

Young Persons Act 1933, s. 50; California Family Code 1994, s. 7540)

In the ﬁrst case, the court may draw a conclusion from certain facts

previously established (Keane 2008, 656); depending on the nature of such

regularities of events, the presumption of fact may shift the burden of

proof or not (Best et al. 1875, 571). In (2) the nature of the presumption is

different, as it is a rule of law, setting forth that the court must draw the

inference that if ﬁve years have elapsed since a person was heard of, that

280 Fabrizio Macagno and Douglas Walton

person is presumed to be dead unless the contrary is proved. In this case,

the burden of proof always shifts. On the contrary, in (3) the burden never

shifts, as the contrary proof is excluded. In this case, the notion of

responsibility is deﬁned by setting an age (see also Park, Leonard and

Goldberg 1998, 106). To be right, following Wigmore, such presumptions

should not be considered as such, but on the contrary as principles of law

(Wigmore 1940, sec. 2491). The crucial distinction therefore rests on the

presumptions of law and presumptions of fact. They are both grounded on

the same probabilistic nature, but while presumptions of law are rules,

presumptions of fact are mere connections grounded on experience or

probability of any kind (Thayer 1898, 314). As Greenleaf put it (Greenleaf

1866, 49; see McBaine 1938, 525):

[Presumptions of fact] are, in truth, but mere arguments, of which the major

premise is not a rule of law; they belong equally to any and every subject-matter;

and are to be judged by the common and received tests of the truth of propositions,

and the validity of arguments. They depend upon their own natural force and

efficacy in generating belief or conviction in the mind, as derived from those

connections, which are shown by experience, irrespective of any legal relations.

The rule of law distinguishes the two types of reasoning essentially equal

as to their epistemic grounding. The dialogical effect is different: While

presumptions of law command an inference in lack of evidence, avoiding

any assessment of the rule of presumption, presumptions of fact need to be

evaluated by the jury before drawing a conclusion.

4.2. Burden Shifting

The second element is the shifting of the burden of proof. Presumptions are

rebuttable in nature (see Hall 1961, 10) and provide only a tentative

conclusion which needs to be relied upon until the contrary is “proved”

(Blackstone 1769, 371), in the sense that the interlocutor fulﬁls the onus

probandi that has been shifted onto him by using the presumption (Best

et al. 1875, 571). This characteristic of presumption can be better described

by the deﬁnition given by Wigmore (1940, sec. 2491):

A presumption, as already noticed, is in its characteristic feature a rule of law laid

down by the judge, and attaching to one evidentiary fact certain procedural

consequences as to the duty of production of other evidence by the opponent. It is

based, in policy, upon the probative strength, as a matter of reasoning and inference,

of the evidentiary fact; but the presumption is not the fact itself, nor the inference

itself, but the legal consequence attached to it. But, the legal consequence being

removed, the inference, as a matter of reasoning, may still remain; and a “presump-

tion of fact,” in the loose sense, is merely an improper term for the rational potency,

or probative value, of the evidentiary fact, regarded as not having this necessary legal

consequence. “They are, in truth, but mere arguments,” and “depend upon their own

natural force and efficacy in generating belief or conviction in the mind.”

281Presumptions in Legal Argumentation

Presumptions, however, are not actual proofs (W. R. R. 1915, 505). Their

only role is the shifting of the burden of proof, as they cannot bring any

evidentiary weight on the conclusion. How and why they shift the burden

of proof, and the nature of the burden, will be examined in detail below.

4.3. Reasoning in Conditions of Lack of Sufficient Evidence

Presumptions cannot be considered as evidence as they are forms of

reasoning that operate when proof is not available, that is, an inference in

conditions of lack of evidence (Louisell 1977, 290). They are not a form of

evidence (Rescher 1977, 1):

To presume in the presently relevant sense of the term is to accept something in the

absence of the further relevant information that would ordinarily be deemed

necessary to establish it. The term derives from the Latin praesumere: To take before

or to take for granted.

As Rescher (1977, 2–3) puts it, presumption is a reasoning in ignorance,asa

lack of evidence is “a circumstance in which one reasons as best one can,

faute de mieux to the resolution of an issue that needs to be settled” (cf. Dascal

2001). Presumptions cannot prove a conclusion: on the contrary, they

intervene when it is not possible to demonstrate a conclusion (Blackstone

1769, 371). A clear example of such a characteristic of presumption comes

from the interpretation of intentions in matters of gifts. In Turchin v. Turchin,

I So.3d, WL 2871564, (2009), the spouses entered into a prenuptial agreement

and, after the marriage, Leslie Turchin acquired two properties with his

premarital assets and took title to each in his and his wife’s name. The

problem was the ownership of the assets after the death of the purchaser. The

presumption is that “a gift is presumed under Florida law when property is

purchased by one spouse but placed in both names.” However, such a

presumption could support the conclusion only if there was a lack of

evidence. As the spouses entered a prenuptial agreement, the situation was

not of lack of evidence and the presumption could not be used.

The relationship between evidence and presumption can be understood

from the legal discussion on the relationship between a presumption and

contrary evidence. The controversial question is whether presumptions

disappear when evidence to the contrary is brought in, or whether they

should be weighed as evidence. A simple case can explain this dialectical

effect. The most classical presumption is the presumption of death: in a

situation in which there is no evidence warranting the conclusion that a

person is dead, he can be presumed to be dead if he has not been heard

from for ﬁve years. However, if the other party in a trial produces some

testimony that the person is actually alive, positive evidence conﬂicts with

the presumption and the court needs to establish whether the testimony or

the presumption prevails. According to the most widely accepted view

282 Fabrizio Macagno and Douglas Walton

(McBaine 1938, 534), such a case needs to be sent to a jury and be evaluated

according to the reliability of the witness. The jury needs to decide whether

they can trust the witness, and only in this case can the testimony be

counted as real proof, as evidence dispelling the presumption. The jury, in

other words, should not weigh a presumption against positive evidence,

but they need to establish whether the evidence produced is real evidence

supporting the opposite conclusion. Presumptions are therefore forms of

reasoning in the case of a lack of evidence: the only way to rebut a

presumption is to produce evidence, namely positive facts that the jury

considers to be relevant and supporting the opposite conclusion (McBaine

1938, 545):

A rebuttable legal presumption is only a rule of law that a fact is judicially decreed

to exist absent evidence to the contrary. In the ﬁrst place then, it should be

constantly borne in mind that the fact is only presumed to exist; that is not a thing

established as ﬁnal, by judicial command. Nor is it something established by

evidence. If it were an established fact, there would be no need to have further

evidence. No problem of weighing would exist.

Presumptions therefore simply assign the jury the task of establishing

whether a proof is a real proof, or rather, of accepting some evidence or not

based on their reasoning.

From these distinctions it may be seen how the nature of the presump-

tion affects the shifting of the burden of proof. While presumptions of law

provide for the burden to shift, presumptions of fact may trigger such a

dialectical effect or not, depending on their strength. How strong an

argument needs to be to prove a conclusion depends on its burden of

proof, which in turn depends on the standard of proof required.

5. The Nature of Presumptions

The relationship between probability and presumption has been acknowl-

edged in several judgments, highlighting how the premise and the con-

clusion in such cases need to be connected by co-occurrence. As set out in

Leary v. United States, “the presumed fact needs to be more likely than not

to ﬂow from the proved fact supporting it” (Leary v. United States, 395 U.S.

6, 36, 1969). This likeliness opens up a crucial question about evaluating

presumptions. If we look back at the history of presumptive evidence, we

notice that presumptions were ﬁrst classiﬁed by Gilbert according to their

strength and their grounds (McBaine 1938, 522–4). The deﬁnition of pre-

sumption he proposes shows a crucial epistemic difference with the other

types of argument or proof (Gilbert 1756, 159–60):

[presumption] is Conjectura ex certo signo proveniens quae alio adducto pro veritate

habetur. When the Fact itself cannot be proved, that which comes nearest to the

283Presumptions in Legal Argumentation

Proof of the Fact is, the Proof of the Circumstances that necessarily and usually

attend such Facts, and these are called Presumptions and not Proofs for they stand

instead of the Proofs of the Fact till the contrary be proved.

This rational connection between events which cannot be considered as a

proof, but simply as a matter of experience, sign and probability, can be

evaluated according to how shared and how probable such a relation is

(Greenleaf 1866, 21):

Presumptions of Law consist of those rules, which, in certain cases, either forbid or

dispense with any ulterior inquiry. They are founded, either upon the ﬁrst prin-

ciples of justice; or the laws of nature; or the experienced course of human conduct

and affairs, and the connection usually found to exist between certain things. The

general doctrines of presumptive evidence are not therefore peculiar to municipal

law, but are shared by it in common with other departments of science. Thus, the

presumption of a malicious intent to kill, from the deliberate use of a deadly

weapon, and the presumption of aquatic habits in an animal found with webbed

feet, belong to the same philosophy, differing only in the instance, and not in the

principle, of its application. The one fact being proved or ascertained, the other, its

uniform concomitant, is universally and safely presumed. It is this uniformly

experienced connection, which leads to its recognition by the law without other

proof; the presumption, however, having more or less force, in proportion to the

universality of the experience.

Presumptions can therefore be evaluated according to the universality of

the experience. However, as the elements of such experience are different

from normal proofs, as presumptions intervene in conditions of lack of

evidence, the factors constituting such probability need to be assessed. In

Gilbert’s view (1756, 159), presumptions can be more or less stringent, or

rather “violent,” “according as the several Circumstances sworn to more or

less usually accompany the Fact to be proved.” In this perspective, pre-

sumptions are inferences from circumstances, and the strength of a pre-

sumption depends on the co-occurrence of the circumstance with the fact.

The strength of a presumption can be classiﬁed as violent, probable and

light. Violent presumptions can be considered as inferences from circum-

stances that necessarily accompany the fact (Gilbert 1756, 160), namely signs.

For instance, if a man is seen running away with a bloody sword from a place

where somebody has been found suddenly dead, he is presumed to be the

murderer, as usually hasty ﬂight accompanies crimes, and the sword and the

blood are signs of a violent action. This type of reasoning was referred to

in the medieval tradition as Undoubted Indicia4(Sarat, Douglas, Merrill

4The roots of the dialogical effect of violent presumption can be traced back to William of

Ockham, who underscored how the presumption that a person remembers what he has

previously learnt strongly supports a conclusion: “Some say [ﬁfth way] that he should be

judged immediately as pertinacious and a heretic of whom there is a violent presumption that

he denies some assertion which he knows is contained in divine scripture or in a determi-

nation of the church. If it can be proved, for example, that he has previously read and

284 Fabrizio Macagno and Douglas Walton

Umphrey, 2007, 32). Such presumptions have their roots in causal connec-

tions. On the contrary, probable presumptions refer only to concomitant

factors. For instance, we can consider the following account distinguishing

the three kinds of presumption (Archbold 1831, 114):

So, upon an indictment for stealing in a dwelling house, if the defendant were

apprehended a few yards from the outer door, with the stolen goods in his

possession, it would be a violent presumption of his having stolen them; but if they

were found at his lodgings, some time after the larceny, and he refused to account

for his possession of them, this, together with proof that they were actually stolen,

would amount, not to a violent, but to a probable presumption merely; but if the

property were not found recently after the loss, as, for instance, not until sixteen

months after, if would be but a light or rash presumption and entitle to no weight.

Plausible presumptions are not signs, but only possible explanations that

can be drawn from how things usually are. While a man who has stolen

some goods needs to have them in his possession just after the theft, only

probability can account for the relation between possession of stolen goods

after a theft and the theft itself.

The older model of strength of presumption is echoed in some codes of

evidence, in which presumptions are distinguished on the basis of their

effect. As Mason (2000–2001, 748–50) puts it, presumptions can be classiﬁed

in three categories (Table 2):

understood in divine scripture or a determination of the church the assertion he denies, or if

it can be proved that previously he had purposefully taught or, even, publicly or secretly

affirmed the assertion he denies. For if it is not probable that such a person has forgotten what he

had previously learnt there is a violent presumption that he knowingly denies catholic truth.

And he should, as a consequence, be considered pertinacious and a heretic” (Dialogus IV, 13).

Table 2 Strengths of Presumptions

Name Effect Example

Weak or Ordinary

Presumptions

Shifting the burden of

presenting evidence

A person is presumed to intend to do what

he does.

Strong presumptions Shifting both the burden of

presenting evidence, and

the burden of persuasion

Where the parties had a ceremonial

marriage it is presumed that they gave

consent and that all essentials existed for

a valid marriage

Very Strong

Presumptions

Shifting both burdens;

enhancing or increasing

the burden to disprove the

presumed fact by a higher

level of persuasion.

Election returns are presumed to be valid

and proper, requiring clear and

convincing evidence to rebut them.

A child born or conceived during a

marriage is presumed to be the legitimate

child of the husband and wife; proof

beyond reasonable doubt is required to

rebut this presumption.

285Presumptions in Legal Argumentation

On this view, the epistemic foundation of the presumption is connected

with its dialogical effects. However, this relationship is not reﬂected in

modern theories on presumption holding the distinction between pre-

sumptions of fact and presumptions of law. As noted above, presumptions

of law can stem either from dialogical policies or from factual reasons (see

also Mueller and Kirkpatrick 1999, 176; Brodin and Avery 2007, 81). In the

ﬁrst case, presumptions are placed on a party in order to facilitate the

production of evidence, while in the second case, presumptions are forms

of inference. A common principle, however, underlies both cases, namely

that the fact presumed or the dialogical condition of having access to

evidence is more likely to be fulﬁlled than the contrary. If we consider the

nature of presumptions of fact and presumptions of law, we can recognize

a common pattern. Presumptions are indirect proof, not testimony or

documents, and stem from the circumstances of a fact, connected to the fact

itself either by an effect-to-cause relation (violent presumptions), or simply

by concomitance (probable presumptions).5We can refer to such types of

presumptions as signs (or causal relations) and concomitances. The two

types of presumptions can be rebutted in different fashions and place a

different burden of proof on the other party.

6. Epistemic Grounds and Dialectical Effects: Rebutting a Presumption

As noted above, presumptions of law and presumptions of fact belong to

the same domain of indirect proof, and the difference between them

consists of the fact that their dialectical effects are governed by a legal

provision. However, the origin of such effects needs to be found in the

nature of presumptions, emerging from the strategies and the conditions of

their rebuttal.

Presumptions admit two different types of rebuttal strategies (Park,

Leonard and Goldberg 1998, 107), that is, challenging the presumed facts

or the foundational fact. For instance, considering the presumption of

death, the other party can either prove that the presumed deceased was

5See Phillipps (1815, 111): “The proof is positive, when a witness speaks directly to a fact

from his own immediate knowledge; and presumptive, when the fact itself is not proved by

direct testimony, but is to be inferred from the circumstances, which either necessarily or

usually attend such facts. It is obvious therefore, that a presumption is more or less likely to

be true, according as it is more or less probable, that the circumstances would not have

existed, unless the fact, which is inferred from them, had also existed; and that a presumption

can only be relied on, until the contrary is actually proved. In order to raise a presumption,

it cannot be necessary to conﬁne the evidence to such circumstances alone, as could not have

happened, unless they had been also attended by the alleged fact,—for that in effect would

be to require in all cases evidence amounting to positive proof;—but it will be sufficient to

prove those circumstances, which usually attend the fact.”

286 Fabrizio Macagno and Douglas Walton

actually heard of during the ﬁve-year period, or produce evidence

that the person is actually alive. The crucial problem is to assess the

effect of the presumption, and the standard of proof needed to rebut the

presumption. According to several legal scholars (for a review, see

Andersen 2003, 112), presumptions are distinguished according to their

strength:

1. mandatory burden-of-pleading-shifting presumptions: If the party proves

A, then the factﬁnder must ﬁnd B, unless the opposing party claims

B is not true;

2. mandatory burden-of-production-shifting presumptions: If the party proves

A, then the factﬁnder must ﬁnd B, unless the opposing party intro-

duces evidence sufficient to prove B is not true. Sufficient evidence

may be deﬁned as any evidence, reasonable evidence, or substantial

evidence.

3. mandatory burden-of-persuasion-shifting presumptions: If the party proves

A, then the factﬁnder must ﬁnd B, unless the opposing party

persuades the factﬁnder that B is not true. Persuasion may be

deﬁned anywhere from a preponderance to beyond a reasonable

doubt.

The crucial epistemic problems lie in the distinction between the burden-

of-production and the burden-of-persuasion shifting presumptions, and the

interpretation of the concept of “production.”

6.1. “Causal” or Rational Connections

The ﬁrst problem can cast light on the crucial connection between the

causal, or logical, foundations and the dialogical effects of presumptions.

The distinction between the two types of burden lies with the strength of

the relationship between facts and conclusions, and it is always established

at the beginning of the trial in civil cases.

In civil cases, presumptions do not really shift the burden of persua-

sion, but rather set it according to considerations different from the

principle that “he who pleads needs to prove.” Strong presumptions of

this kind are, for instance, the presumption against suicide (the death of

the insured was not due to suicide, but accidental). These are grounded

on human experience and human nature (Boos 1945, 798), even if there

is no direct causal connection between death and not-suicide. If we

analyze the Codes of Evidence of the various states, we notice how

presumptions are distinguished according to their purpose and founda-

tion. In the Florida Evidence Code (2005), in particular, presumptions shift-

ing the burden of proof (or rather setting it) need to be established “to

287Presumptions in Legal Argumentation

implement public policy” and not simply to facilitate the determination

of a particular action (90.303). An interesting example comes from the

presumption concerning the burden of proof, that is, undue inﬂuence in

inter vivos or testamentary gifts. This presumption has been explained on

the basis of a strong social policy (In re Estate of Davis, 428 So. 2d 774,

775–76, Fla. 4th DCA, 1983), and in particular on the grounds that older

persons need to be defended against ﬁnancial exploitation by those they

rely upon and trust. Undue inﬂuence is “rarely susceptible of direct

proof,” because in cases of testamentary gifts the decedent never testiﬁes

the contrary, and the entire proof rests on the self-serving testimony of

the alleged wrongdoer (Nilsson 2003). The dialectical reason for incre-

menting the burden of proving the absence of inﬂuence is in this case

combined with the purpose of avoiding potential crimes and defending

the weaker party.

The relationship between rational connections and dialectical effects can

be found in criminal law. In criminal cases there is no presumption

stronger than the presumption of innocence, and presumptions cannot

reverse the burden of proof (Martin, Capra and Rossi 2003, 94; Sandstrom

v. Montana, 442 U.S. 510, 517–8, 1979). As a result, in criminal cases there

is no burden-of-persuasion shifting presumption; presumptions are not

mandatory, but may simply assist the prosecution by relieving them of the

burden of proving all the elements of the offence (such as knowledge or

intent), without being conclusive or warranting directly the truth of the

conclusion (Francis v. Franklin, 471 U.S. 307, 307, 1985).6However, such

presumptions need to be grounded on a rational connection, and not

simply on statistical probability (Tot v. United States, 319 U.S. 463, 467–8,

1943).

6.2. Rational, Inductive and Dialogical Presumptions

Crucial problems in presumption evaluation stem from uncertain civil

cases in which the type of presumption has not been stated by law. Such

cases are governed by a default federal rule, FRE 301, that is included in

the legislations of all states. According to FRE 301, presumptions only shift

the burden of production: when a presumption is governed by this default

rule for civil cases, it has the effect of shifting on to the other party the

burden of producing contrary evidence. However, what counts for

6Usually some presumptions are incorrectly regarded as presumption-shifting, such as the

presumption of intoxication for people found with a blood-alcohol percentage of 10/100. In

such cases, presumptions are never mandatory, but only permissible (Taylor and Oberman

2006, 33–5)

288 Fabrizio Macagno and Douglas Walton

“evidence” is often interpreted by the local jurisdictions, and sometimes

read as “introducing any kind of evidence,” sometimes as “proving that

the nonexistence of the presumed fact is more probable than its existence”7

(for the interpretation problem, see United States v. Jessup, 757 F.2d 378, 1st

circ., 1985).

Best (2009, 229–30) noted how the interpretation of the effects of pre-

sumption differ from state to state. The literature on the rebuttal of

presumptions in civil law (see for instance Hecht and Pinzler 1978; Park,

Leonard and Goldberg 1998, 102–5) distinguished between different

theories of interpretation of this rule, namely the bursting bubble

(see McCormick 1972, 871), the burden of persuasion shifting, and an

intermediate theory (see Morgan 1933). In the ﬁrst case, the presumption

simply disappears when evidence of any kind is brought in; in the

second case, presumptions alter the burden of persuasion and need to be

rebutted by a standard of proof; in the third case, evidence needs to be

real evidence, namely it should be considered by the jury or the judge

as sufficient (see Mueller and Kirkpatrick 1999, 182–90). If we look at the

local interpretations of this general rule, we can notice how different

theories are often applied to different types of presumption, depending

on their grounding and their reasons (Craig Lewis 1995, 20). This

view is based on an analysis of the different grounds of presumption

(Cleary 1984, 968–9), that act alone or in combination with other

reasons:

1. to correct an imbalance resulting from one party’s superior access to

the proof;

2. for notions, usually implicit rather than expressed, of social and

economic policy that incline the courts to favor one contention by

giving it the beneﬁt of a presumption, and correspondingly to handi-

cap the disfavored adversary;

3. to avoid an impasse, to some result, even though it is an arbitrary one;

4. probability: the judges believe that proof of fact B renders the infer-

ence of the existence of fact A so probable that it is sensible and

timesaving to assume the truth of fact A until the adversary disproves

it.

When the purpose of presumption is only to facilitate the determination of

a speciﬁc case, such a presumption is dispelled by the simple introduction

of any kind of evidence; when instead matters of probability or public

policy intervene, then burden shifting may be considered.

7FRE 301. Notes of Committee on the Judiciary, House Report No. 93–650.

289Presumptions in Legal Argumentation

6.3. Evaluating Presumptions

The different nature of presumptions arises also in relation to conﬂicting

presumptions. In criminal cases, the most signiﬁcant cases of conﬂicting

presumptions concern the alleged shifting of the burden of persuasion. The

burden of persuasion can be never defeated by any other presumptions,

unless such presumptions are grounded on serious policies of public

interest (State v Coetzee, 2 LRC 593, 677, para 220, 1997). A leading case is

R v DPP, ex parte Kebilene (2 AC 326, 2000), in which the presumption of

innocence conﬂicts with the presumption of guilt:

(1) A person is guilty of an offence if he has any article in his possession in

circumstances giving rise to a reasonable suspicion that the article is in his

possession for a purpose connected with the commission [. . .] of acts of terrorism

[. . .] (3) It is a defence for a person charged with an offence under this section to

prove that [. . .] the article in question was not in his possession for such a purpose

[. . .].

In such a case, the burden is on the accused, but the presumption of guilt

prevails because of a potential prejudice of the public interest (for the

reverse onus and the reasons underlying such a presumption, see Hoffman

and Rowe 2010, 216–7).

In civil cases (Mueller and Kirkpatrick 1999, 190–2), most theories

support the view that the presumption grounded on stronger reasons of

policy and logic shall prevail, even though such comparisons are only

rarely made by the court (Louisell 1977, 295). A clear example is given by

Sillart v. Standard Screen Co. (119 N.J.L. 143, 194 A. 787, 1937); in this case,

two presumptions grounded conﬂict in different ways: the presumption of

continuation of life and the presumption of validity of a common law

marriage arising upon the consummation thereof. The facts can be sum-

marized as follows:

On May 27th, 1916, Anna Sillart had entered into a ceremonial marriage with a

Hans Rekand who disappeared in 1923 and has neither been seen nor heard from

since that time. Five years after Rekand’s disappearance, in 1928, although the

Rekand marriage was not dissolved, she effected a common law marriage with

decedent with whom she, together with one son by Rekand, lived until decedent’s

death.

In this case, the presumption grounded on public policy was found to

prevail over a presumption based on probability and experience. In this

perspective, the epistemic foundation on logical reasons or simply on

statistical connections plays a fundamental role in determining the effects

of a presumption, that led to a tentative classiﬁcation in O’Dea v. Amodeo

(118 Conn. 58, 170. Atl. 486, 1934), represented in Table 3 below:

290 Fabrizio Macagno and Douglas Walton

However, in such cases, presumptions based on social policy are not

considered.

The last feature of presumptions can be shown by considering cases of

conﬂicting equipollent presumptions. In Westdeutsche Landesbank Girozen-

trale v. Islington London Borough Council (A.C. 669. TOP, 1996), a voluntary

payment was made, raising a presumption of a resulting trust, that is, a

trust settled for the purposes of holding the money on trust. The problem

arose in consideration of the conﬂicting presumption, that is, that advance-

ment was made. While the voluntary payment raises the presumption of

a non-gift, the advancement leads to the conclusion that the sum was in

fact a gift. The two presumptions are on the same level considering their

grounds; however, they reﬂect different orders of plausibility. The trust can

be presumed from a voluntary payment only if advancement cannot be

presumed (Ong 2007, 401–2). In such cases, the impossibility of a pre-

sumption is a presupposition of the other presumption.

Considering the above-mentioned policies, it may be noted that the force

and the strength of a presumption, or rather its “violence,” adopting the

old terminology, stem from epistemic considerations. Presumptions arise

from dialectical, causal or statistical reasons, and, as it emerges from the

civil law rules, dialectical reasons give rise to presumptions weaker than

the ones stemming from logical or probabilistic grounds. Considering the

criminal law, it may be noted how the type of connection is a crucial

element that distinguishes statutory from non-statutory presumptions. The

rational, or logical, connection carries a different effect on the dialogical

situation than foundations that are dialectical or inductive in nature.

The function of making a presumption is to enable argumentation to

move forward without getting continually bogged down by having to

Table 3 Epistemic foundations of presumptions and their effects

Epistemic foundation Purpose Dialogical effect

Convenience

(presumption

of sanity)

To bring out the real issues

in dispute, thus avoiding

the necessity of producing

evidence as to matters not

really in issue.

Criminal: The State might rest upon it as

making out a prima facie case until

evidence to the contrary is introduced

Civil: The presumption operates only until

the defendant has produced substantial

countervailing evidence, that is evidence

sufﬁcient to raise an issue

Common experience

and inherent

probability

Common experience and

reason justify the drawing

of a certain inference from

the circumstances of a

given situation.

It exhausts itself when the defendant

produces substantial countervailing

evidence

Dialogical reasons The circumstances involved

in an issue are peculiarly

within the knowledge of

one party.

In certain instances the law deems it ﬁt that

the burden should be on him not merely

to offer some substantial countervailing

evidence but to prove such circumstances

291Presumptions in Legal Argumentation

prove a proposition as part of an argument required to help the investi-

gation move forward. The problem may be that proving such a proposition

may be too costly, or may even require stopping the ongoing discussion or

investigation temporarily so that more evidence can be collected and

examined. The problem is that a particular proposition may be necessary

as a premise in a proponent’s argument that has been put forward, but the

evidence available at present may be insufficient to prove it to the level

required to make it acceptable to all parties. Hence the attempt to move

forward with the argumentation may be blocked while the opponent

demands proof. The two parties may then become locked into an evidential

burden of proof dispute in which one party says “you prove it” and the

other says “you disprove it.” This interlude may block the ongoing

discussion. A way to solve the problem is for the proponent or a third party

to say, “Let’s allow this proposition to hold temporarily as a premise in the

proponent’s argument, so that we can say he has proved his contention

well enough and we can accept the conclusion of his argument tentatively

as a basis for proceeding.” If necessary, later on, the sub-discussion can be

continued by bringing in more evidence for or against the proposition

serving as the premise.

7. Rebutting the Grounds of Presumptions

As noted above, presumptions can be rebutted by challenging the foun-

dational facts or the conclusion of the inference based on the presumption

(interpreting presumption as the rule of presumption). Challenging the

presumption rule would be pointless in both presumptions of law and

presumptions of fact. In the ﬁrst case, it would amount to challenging a

law; in the second case, it would be meaningless to prove the defeasibility

of an inference which by nature is rebuttable. Problems concerning pre-

sumptions arise when the case rests on the inference from witness state-

ments to the truth of the testimony. In law, such an inference is warranted

by the presumption that a witness is presumed to speak the truth, and

therefore this kind of testimony can be rebutted by showing that the

witness is not truthful. More speciﬁcally, the evidence can be questioned by

raising doubts about various factors (Mont. Code Ann. § 26-1-302; cf. Cupp

v. Naughten, 414 U.S. 141, 1973:

(1) the demeanor or manner of the witness while testifying;

(2) the character of the witness’s testimony;

(3) bias of the witness for or against any party involved in the case;

(4) interest of the witness in the outcome of the litigation or other motive

to testify falsely;

(5) the witness’s character for truth, honesty, or integrity;

292 Fabrizio Macagno and Douglas Walton

(6) the extent of the witness’s capacity and opportunity to perceive or

capacity to recollect or to communicate any matter about which he

testiﬁes;

(7) inconsistent statements of the witness;

(8) an admission of untruthfulness by the witness;

(9) other evidence contradicting the witness’s testimony.

These factors can be structured as critical questions matching an argumen-

tation scheme for argument from witness testimony. Recent studies on

argumentation and law (Wyner and Bench-Capon 2007; Gordon and

Walton 2009; Bex et al. 2003) have shown how the underlying logic of legal

reasoning can be described by using argumentation schemes representing

prototypical patterns of defeasible inference that can shift a burden of

proof from one party to the other in argumentation about a disputed claim

(Bench-Capon and Prakken 2010; Prakken and Sartor 2006). The link

between presumption and rebuttal is provided by argumentation schemes,

abstract and prototypical patterns of inference (see Walton, Reed and

Macagno 2008; Kienpointner 1992; Grennan 1997; Perelman and Olbrechts-

Tyteca 1969).

We can represent the structure of the scheme for argument from witness

testimony as follows (Walton 2008a, 45):

POSITION TO KNOW PREMISE: Witness Wis in position to know

whether Ais true.

TRUTH TELLING PREMISE: Witness Wis telling the truth (as Wknows

it).

STATEMENT PREMISE: Witness Wstates that Ais true (false).

GENERALIZATION: If a witness W is in a position to know whether A

is true or not, and W is telling the truth (as W knows it), and W states

that A is true (false), then A is true (false).

CONCLUSION: Therefore (defeasibly) Ais true (false).

The acceptability of the argument centrally depends on the two factors: the

truth telling premise, and the generalization. However, what is the truth?

Obviously the witness can only report what he or she recollects, and the

truth of his or her statements shall be interpreted as truth in reporting his

or her own memories that can be assessed during cross-examination.

However, the weakness of the reasoning depends on the generalization,

linking memories, which can be faulty or defective, to truth. Even if all

knowledge-related factors, such as ability to recollect and testify, or truth-

telling elements, such as being unbiased, are proved, the argument is still

defeasible (United States v.Khadr, Mot. for App. Relief, (D-084), Sep. 31,

2008). Memories are reconstructions that can differ from reality, and can be

inﬂuenced during cross-examination or altered over the years by similar

293Presumptions in Legal Argumentation

experiences. However, the strength of the presupposition on which the

presumption of truth is based, that is, that memory reﬂects the truth,

cannot be questioned or attacked (States v. Carter, 410 F.3d 942, 950–51, 7th

Cir., 2005), holding that expert testimony on memory reliability is not

needed), but only contrasted with the different presumption that memory

fades over the years (United States v. Rosenberg, 297 F.2d 760, 763, 3d Cir.,

1958).

We now illustrate more generally how schemes represent common

evidential reasoning in law of a kind that is defeasible and that depends

on presumptions. The following argumentation scheme represents argu-

ment from expert opinion (Walton and Reed 2003, 200):

MAJOR PREMISE: Source Eis an expert in subject domain Scontaining

proposition A.

MINOR PREMISE: Easserts that proposition A(in domain S)istrue

(false).

CONDITIONAL PREMISE: If source Eis an expert in a subject domain

Scontaining proposition A, and Easserts that proposition Aistrue

(false), then Amay plausibly be taken to be true (false).

CONCLUSION: Amay plausibly be taken to be true (false).

This scheme represents the relation between the ethos and knowledge of

the person expressing an opinion, and the reliability or acceptability of his

or her opinion. The premise “If Eis an expert, then his or her opinion may

be plausibly taken to be true” is commonly accepted, and the reasonable-

ness of the inferences based on such a scheme depends on how we classify

a person as an “expert.”

If we analyze schemes frequently used in law such as the argument from

classiﬁcation, or argument from cause to effect, or argument from analogy,

it may be seen that they are characterized by an epistemic principle, based

on the concept of classiﬁcation, and in turn sometimes based on deﬁnition.

These concepts are embedded in common patterns of legal reasoning.

Consider the following examples (Gray 2002, 7):

Case 1. Classiﬁcation: Modus ponens

The Keppel videotape shows the 73rd Home Run ball enter the webbing

of the Plaintiffs’ softball glove and stay there for approximately six-

tenths of one second before the ball, the glove, and Mr. Popov disappear

behind the head of another spectator. The Plaintiff has proposed a

deﬁnition of “catch” that would direct the Court to ﬁnd ﬁrst possession

and award title based on this evidence. “Popov’s catch is the single

controlling element determining possession and ownership. Once the

baseball entered Popov’s glove, the fate of the baseball was sealed.”

(Plaintiff’s Trial Brief at 20).

294 Fabrizio Macagno and Douglas Walton

Case 2. Classiﬁcation: Analogical inference8

(case: conjoined twins) I was at ﬁrst attracted by the thought prompted

by one of the doctors, that Jodie was to be regarded as a life support

machine and that the operation proposed was equivalent to switching off

a mechanical aid. Viewed in that way previous authority would catego-

rize the proposed operation as one of omission rather than as a positive

act.

Case 3. Classiﬁcation: Modus tollens9

Milkovich, a high school wrestling coach, sued Lorain Journal Compa-

ny’s newspaper for publishing a column stating that “Anyone who

attended the meeting...knows in his heart that Milkovich [. . .] lied at

the hearing [. . .]” (Milkovich, 497 U.S. at 5, 110 S. Ct. at 2698, 111 L. Ed.

2d at 9). The statement was classiﬁed as “defamatory,” as it damaged the

petitioner’s reputation. The shared deﬁnition of “defamatory” presup-

poses the existence of a false statement, stated with malice, damaging

someone’s reputation. The respondent did not choose to prove that the

assertion was in fact true (harder to prove), but that the assertion could

not be veriﬁed, as it reported an opinion and not a fact. Under the First

Amendment “there is no such thing as a false idea” (Gertz v. Welch, 418

U.S. 323, 1974).

In Case 1, a plausible modus ponens is used, which can be represented as

follows:

• “to catch” means to take hold of an object (whether for a nanosecond

or less);

• Popov captured the ball for six-tenths of a second;

• as a result, he caught the ball.

The plausibility of the conclusion depends only on the plausibility of the

deﬁnition, which may be more or less accepted or acceptable. The conclu-

sion follows necessarily from the premises according to the deductive

axiom, but the conclusion is rebuttable as the deﬁnitional premise is

defeasible. In the second case, the same semantic principle, namely clas-

siﬁcation, is combined with analogical reasoning, in which a new generic

concept (“entity able to provide life support”) is ﬁrst abstracted from the

entities compared, considering only one of their possible functions; such an

abstracted concept licences the attribution of the predicate (“to be a

positive act / an omission”); ﬁnally the predicate is attributed to the

8Re A (Children) (Conjoined Twins: Surgical Separation), 4 All ER 961 (2001), Fam 147, at 249.

9Milkovich v.Lorain Journal Co., 497 U.S. 1 (1990).

295Presumptions in Legal Argumentation

second entity (“killing one of the two conjoined twins is a positive act / an

omission”) (see Macagno and Walton 2009).

As seen in the sections above, presumptions are based on two types

of groundings: value judgments (social or dialogical policies), and logic

and experience (or causal connections and probability) (Louisell 1977,

296). Social policies are often interlaced with probabilities different in

nature, and the effect or strength of a presumption essentially depends

on such considerations. However, if a presumption disappears or is

rebutted by evidence or another presumption, the principle on which it

is based is never affected, nor is the principle, even the strongest one, a

necessary condition for establishing the prevalence of a presumption

over the other. Convenience, public policy, dialectical considerations and

possibility or rational connection are not necessary or sufficient condi-

tions, but simply epistemic justiﬁcations of reasoning in lack of evidence.

If the defendant is presumed guilty for reasons of social policy, the

principle of fairness underlying the presumption of innocence is not

breached, but simply weighed against a different and stronger reason

(Hoffman and Rowe 2010, 216–22).

8. Conclusion

Our analysis has shown that the notion of presumption has to be

deﬁned on two levels: an inferential level and a dialectical level. At the

inferential level, a presumption is deﬁned as an inference to the accep-

tance of a proposition from two other propositions called a fact and a

rule. At the dialectical level, presumption is best modeled as a speech act

put forward by parties in a dialogue during the argumentation stage

where the two parties to the dispute are putting forward arguments in

response to the arguments and other moves of the other party. At the

dialectical level, a presumption is deﬁned in terms of its use or function

in a context of dialogue. This function is to shift an evidential burden

from one side to the other in a dialogue, where the effect of such a shift

is on the burden of persuasion established at the opening stage of the

dialogue.

We can summarize our ﬁndings by citing the six essential characteristics

of presumptions:

1. Presumptions are used in dialectical situations where one party puts

forward an argument that is not strong enough to meet the standard

of proof required to accept it.

2. The argument in question is nevertheless a worthy argument and

should be taken into account because it provides some relevant

evidence that is important.

296 Fabrizio Macagno and Douglas Walton

3. Presumptions provide tentative support, directed at achieving differ-

ent purposes, but are ultimately aimed at allowing the parties to move

forward in an investigation that may provide the necessary positive

evidence.

4. Presumptions can bring about different dialogical effects depending

on the purpose for which they have been introduced.

5. Every presumption is aimed at achieving a speciﬁc goal, which can be

dialectical (deciding an issue on the basis of the arguments pro and

contra), social (defending the interests of a particular group of

people), or political (promoting a particular policy pro or against

speciﬁc behaviours).

6. A presumption disappears on the provision of sufficient evidence to

prove or refute the proposition presumed.

How the last characteristic works is controversial in law. There are two

theories (Park, Leonard and Goldberg 1998, 109–12). The question of

precisely how presumptions are refuted is left as a problem worth further

research and study.

Fabrizio Macagno

Universidade Nova de Lisboa

ArgLab

Institute of Philosophy of Language (IFL)

Avenida de Berna 26

1069-061 Lisbon

Portugal

E-mail: fabrizio.macagno@fcsh.unl.pt

Douglas Walton

University of Windsor

CRRAR 2500 University Ave. W.

Windsor, Ontario

N9B 3Y1 Canada

E-mail: waltoncrrar@gmail.com

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Robert C. Pinto

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Jan 2006

Nicholas Rescher

Presumption is a remarkably versatile and pervasively useful resource. Firmly grounded in the law of evidence from its origins in classical antiquity, it made its way in the days of medieval scholasticism into the theory and practice of disputation and debate. Subsequently, it extended its reach to play an increasingly significant role in the philosophical theory of knowledge. it has thus come to represent a region where lawyers, debaters, and philosophers can all find some common around. in Presumption and the Practices of Tentative Cognition, which was originally published in 2006, Nicholas Rescher endeavors to show that the process of presumption plays a role of virtually indispensable utility in matters of rational inquiry and communication. The origins of presumption may lie in law, but its importance is reinforced by its service to the theory of information management and philosophy.

The Indulgence of Reasonable Presumptions: Federal Court Contractual Civil Jury Trial Waivers

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