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Nonfallacious arguments from ignorance

Volume 29, Number 4, October 1992
argument from ignorance has tradi-
tionally been classified as a fallacy, but there
is growing recognition that this kind of argu-
ment can be nonfallacious in some cases.
This raises a question: what kind of success-
ful or good argument is it, in these cases? In
this paper two argumentation schemes to
represent the form of the
argumentum ad ig-
are introduced. It is argued that
they are best judged as fallacious or not in a
particular case, in relation to a context of use
in dialogue.
The fallacy of the argument from igno-
(argumentum ad ignorantiam),
ing to Copi and Cohen (1990, p. 93) is "the
mistake that is committed whenever it is ar-
gued that a proposition is true simply on the
basis that it has not been proved false, or that
it is false because it has not been proved
true." But is this kind of argument a fallacy?
It has been argued in Woods and Walton
(1978) that it is, generally, even though there
are some cases where it is not.
Copi and Cohen (p. 94) provide an exam-
ple that suggest that, at least in some cases, it
is not.
Case 1: In some circumstances, of course, the
fact that certain evidence or results
have not been got, after they have been
actively sought in ways calculated to
reveal them, may have substantial ar-
gumentative force. New drugs being
tested for safety, for example, are com-
monly given to mice or other rodents
for prolonged periods; the absence of
any toxic effect upon the rodents is
taken to be evidence (although not
But if the argument from ignorance is non-
fallacious in this case, what kind of argument
is it?
What species of correct (good, reason-
able) argument is it?
In some cases, the
argumentum ad ig-
a correct (nonfallacious) argu-
ment because we can rightly assume that our
knowledge base is complete. If some propo-
sition is not known to be in it, we can infer
that this proposition must be false.
Case 2: The posted train schedule says that
train 12 to Amsterdam stops at Haar-
lem and Amsterdam Central Station.
We want to determine whether the train
stops at Schipol. We can reason as follows:
since the schedule did not indicate that the
train stops at Schipol, we can infer that it
does not stop at Schipol. In other words, we
can presume that the knowledge base is com-
plete (epistemically closed) on the ground
that if there were additional stops, they
would be specified on the schedule posted.
Perhaps we could even know that this knowl-
edge base is complete, by knowing that the
railway policy is to be sure that if the train
Douglas Walton
conclusive evidence) that the drug is
probably not toxic to humans. Con-
sumer protection often relies upon ev-
idence of this kind. In circumstances
like these we rely not on ignorance but
upon our knowledge, or conviction,
that if the result we are concerned
about were likely to arise, it would have
arisen in some of the test cases. This use
of the inability to prove something true
supposes that investigators are highly
skilled, and that they very probably
would have uncovered the evidence
sought had it been possible to do so.
stops at a particular station, the name of that
station is always marked on the posted
schedule. The basic principle at work here is
what de
(1988, p. 182) calls
the principle, "If it were true, I
would know it."
Epistemic Closure.
If one knows that it cannot
be the case that
without his knowing it, then,
if not -
, he can infer that not -
The example de Cornulier gives (p.182) is
the following: "If it were raining, I would
know it; now, it is not the case that I know
that it is raining; therefore, it is not raining."
This principle of inference is rightly called
epistemic closure because once a knowledge
base is definitely closed, then if a proposition
does not appear in it, we can conclude that
this proposition is false.
It is a kind of inference that takes the form
of an epistemic counterfactual: if
true, it would be in my knowledge base; but
is not in my knowledge base; therefore
is false. It is an
ad ignorantiam
argument but,
apparently a principle of epistemic reason-
ing that could be quite correct and reasonable
in many cases of everyday argumentation.
In other cases, however, the
ad ignorantiam
can be a fallacy precisely be-
cause the knowledge base is incomplete in a
relevant respect.
Case 3: According to Benoit (1990, p. 25),
some of Aristotle's works on rheto-
ric-e.g. the
Synagoge Technon,
and the
not ex-
tant: "Hence, the absence of a topic
from the surviving corpus .... is insuffi-
cient evidence that [Aristotle] failed to
discuss it."
(1975, p. 398), a computer program called
SCHOLAR is asked whether rubber is a
product of Guyana.
Case 4: SCHOLAR does not have any specific
item of knowledge saying that Guyana
produces rubber or not. However,
SCHOLAR does know that Peru and
Colombia are the major rubber produc-
ers in South America. And SCHOLAR
also knows that rubber is an important
product, so if Guyana did produce rub-
ber, SCHOLAR would presumably
know it. SCHOLAR concludes: "I
know enough that I am inclined to be-
lieve that rubber is not an agricultural
product of Guyana" (p.398).
In this case, SCHOLAR's nonfallacious
ad ignorantiam is
warranted by
an epistemic counterfactual; if this proposi-
tion were true, I would know it. SCHOLAR
argues from ignorance nonfallaciously: I do
not know that this proposition is true; there-
fore, it is false.
In a case like this, absence of knowledge is
significant because of a presumption that if a
particular proposition were true, it would be
known to be true. But it is a kind of shaky
reasoning or guesswork. It would be incor-
rect to say that you
the proposition in
question to be false (beyond doubt). Rather,
you can say it is a reasonable presumption to
infer, based on what you know.
In this case, our list of the topics that Aris-
totle wrote on, in the subject of rhetoric, is
incomplete. Hence, as Benoit warns, it would
be an erroneous inference to conclude that
Aristotle failed to discuss a topic, simply on
the basis of the absence of a discussion of
that topic in his known writings.
In still other cases, however, our knowl-
edge base may be incomplete in a relevant
respect, but we can still argue non-
fallaciously from ignorance, on the basis of
intelligent guesswork. In the following case
from Collins, Aiello, Warnock and Miller
It would seem that in case 4, and case 1 as
well, the argument from ignorance involves
a kind of practical reasoning, of the type an-
alyzed in Walton (1990), that goes forward in
argument as licensing a tentatively reason-
able conclusion, acceptable on a basis of bur-
den of proof. It may be useful to go ahead
and licence the drug in question, in case 1,
for example, on the grounds that it can save
lives or help in medical treatment, provided
there is no evidence, that has yet arisen, to
show that it is harmful to humans.
Whatever kind of reasoning this is, it is
clear that it is a species of
nonmonotonic rea-
subject to default in the sense that if
new evidence should come into consider-
ation, in the future, that shows the conclu-
sion to be false, it must be given up.
words, this kind of reasoning licences an arguer
to accept a proposition as true (or false) pro-
visionally, subject conditionally to future ev-
idence that may arise in the future
investigations or argumentation-see Reiter
(1987). It is a kind of presumptive reasoning
that can be correct (or at least not incorrect)
in some cases.
In case 1, the basis of the reasoning is the
presumption that the investigators would have
been likely to turn up some evidence of toxic-
ty, if it existed, because they are skilled, and
because they have done some thorough or se-
rious investigations already. This is an expecta-
tion, an initial presumption that, in the context,
allows the drawing of a presumptive conclu-
sion of safety that in turn licenses a policy or
prudent course of action, in the circumstances.
Presumption is a speech act halfway be-
tween assertion and (mere) assumption or
supposition in argument. The key thing
about presumption as a speech act in a con-
text of dialogue is that it reverses the initial
burden of proof. In the case above, initially
the burden of proof was on the side advocat-
ing the use of the drug for treatment of
human subjects, on grounds of safety, or dan-
ger to human life. Given the presumptions
raised by the current level of testing and in-
vestigation of the effects of the drug, how-
ever, the argument from ignorance licences
the drawing of the presumptive conclusion
by reversal of this burden. Anyone who
claims that the drug is too dangerous or toxic
to be used on humans is now obliged to step
forward and present some new evidence to
this effect. Otherwise the presumptive infer-
ence (argument from ignorance) goes ahead.
How presumptive argument can be rea-
sonable in some cases as a species of non-
monotonic reasoning is best analyzed
pragmatically by understanding how the fol-
lowing sequence of speech acts is used to
shift a burden of proof in a dialogue ex-
change between speech partners. There are
nine speech act conditions.
There is a context of dialogue, e.g. a critical
discussion or scientific investigation, in-
volving two arguers or sides, called the
"proponent" and the "respondent."
A particular proposition
would be a
useful assumption to help the argumenta-
tion in the dialogue move forward.
The proponent brings
forward explicitly
for acceptance, or his argument implicitly
brings it forward, ie., as a non-explicit
The respondent has an opportunity to re-
If the respondent fails to reject
, then
becomes a commitment or concession of
both parties.
If later, the respondent wishes to retract
as a commitment, she can do so by bring-
ing forward evidence against
Once having accepted
, the respondent
is obliged to let
stay in place provision-
ally, for the purpose of continuing the di-
Prior to the respondent's acceptance of
the burden is on the proponent to provide
evidence in favor of
, or practical reasons
for accepting
After the respondent's acceptance of
the burden is on her to give evidence, or
sufficient reasons to dislodge
as an ac-
ceptable commitment.
This analysis of presumption clearly itself
presumes the existence of a dialectical
framework for the evaluation of arguments
where two parties "reason together." But
such a framework is given in the outline of
formal dialectic presented by Hamblin
(1970, chapter 8), and in more recent works
like van Eemeren and Grootendorst (1984)
One context of dialogue is that of the in-
quiry, where the goal is to prove that a partic-
ular proposition is true (or false), or that it
cannot be proved true (or false) by evidence
based on premises known to be true. The
inquiry has a particular burden or standard
of proof that has to be met for a conclusion to
be proved. Once that standard is met, the
inquiry is closed, and the burden of disproof
is cast onto anyone who would raise ques-
tions to challenge or re-open the inquiry.
In case 1 for example, once a new drug has
been tested thoroughly enough to meet a
standard considered sufficient for human
safety, a decision may be made to go ahead
and licence the drug for use. The inquiry is, at
least provisionally, closed. But should new
evidence come in from users of the drug that
raise serious questions about its safety, the
inquiry may be re-opened.
Another context of dialogue is that of the
where the goal is to re-
solve a conflict of opinions by rational argu-
mentation. The goal of each participant is to
prove his thesis is right, using arguments based
on premises that are accepted by the other
side. The thesis of this party is a proposition
that conflicts with, or is opposed to, the point
of view of the other party in the discussion.
Case 3, for example, could be in the con-
text of a critical discussion of whether
Artistotle discussed a particular topic in
However, both parties might accept
that Artistotle wrote some works on rhetoric
that are not extant. Suppose one of the par-
ties in the discussion were to try to use the
argument that Aristotle failed to discuss a
particular topic on the grounds that she
could not find this topic in the writings of Ar-
istotle that she analyzed. The other party could
reject this argument from ignorance, with justi-
fication, given that there is prior agreement, or
agreement can be presumed to be reachable,
on the historical finding that Artistotle may
have written works on rhetoric that are not
Presumably, such a historical finding
would be relevant to the critical discussion
because it is the result of a prior inquiry that
has been widely accepted, and that the par-
ticipants would not be prepared to dispute
(in the context of their present discussion).
In such a case, we could say that the critical
discussion is functionally related to an in-
quiry in such a way that certain results of the
inquiry can be taken as agreed-upon
knowlege for the purpose of the critical dis-
cussion. Van Eemeren and Grootendorst
(1984, pp.
call this aspect of a critical
discussion an
intersubjective testing proce-
(ITP) where sources of knowledge (like
an encyclopedia or dictionary) can be intro-
duced into the critical discussion to provide
information or knowledge acceptable to
both participants. An ITP can function to tilt
burden of proof in a critical discussion to one
side or the other.
Whether the
argumentum ad ignorantiam
is fallacious or not, in a given case, can be
seen then as depending on how it was used in
the context of dialogue for that particular
case. Such standards of correctness depend
on an allocation of burden of proof, telling us
what constitutes a successful proof for that
type of dialogue in the given case. So con-
ceived, the
argumentum ad ignorantiam
be nonfallacious in some cases, and its being
judged as correct in such cases depends on
pragmatic standards of correctness of use of
an argument in a context of dialogue.
It seems fair to conclude that the argu-
ment from ignorance is, in some cases, a rea-
sonable kind of argument, and no
necessarily fallacious. It is an epistemic type
of argument, but in many cases the conclu-
sion one is warranted to infer is not a knowl-
edge claim. Instead, it is a defeasible
(default) conclusion based on a sequence of
presumptive reasoning. The premises in this
sequence of reasoning are not known to be
true (or false), but are presumed to be true
(or false) on the basis of what one would
normally expect the reasoner to know, given
the depth of his, her or its knowledge base,
and other circumstances of the case. And,
indeed, if we can accept the above analysis of
presumptive reasoning as a legitimate kind
of argument, used in a context of dialogue, it
possible to see how the argument from
ignorance works as a species of correct argu-
ment. "Correct" here means a kind of argument
that is used properly to fulfil requirements of
burden of proof in a context of dialogue.
The argument goes forward tentatively on
a practical basis, advocated by a proponent,
subject to refutation by evidence that can be
introduced by a respondent in dialogue. This
kind of presumptive reasoning is best seen not
as a competitor or usurper to knowledge-
based reasoning, but as a useful temporary al-
ternative, in cases where existing knowledge is
not completely sufficient to resolve a practi-
cal conflict requiring an action or opinion.
There is a question about what counts as an
argument from ignorance. For typically, in
these cases-especially in case 2-there is some
existing knowledge, so the argument is not, at
least completely, an argument from ignorance.
Also, a negative result, finding that something
did not happen, is often described as knowledge.
Again, especially in case 2, the absence of a
proposition could be described as a kind of
knowledge that it is false. As Copi and Cohen
put it, in case 1: "In circumstances like these
we rely not on ignorance, but upon our knowl-
edge, or conviction, that if the result we are
concerned about were likely to arise, it would
have arisen in some of the test cases." Even if
such a negative finding can be properly de-
scribed a kind of knowledge, in some cases, it
can still be justified to classify the argument
as an
ad ignorantiam
in a broad
spectrum of
in everyday argumentation,
because it is based on presumption or "convic-
tion" that goes forward in the absence of com-
plete knowledge.
Where epistemic closure is
to warrant a conclusion as "known to
be true," it is often
useful and correct
to draw a presumptive conclusion, not by closure
but by default. It is not an argument from total
ignorance, but an argument from partial igno-
rance, where the existing or available knowledge
to resolve the practical problem,
or settle the issue beyond continuing doubts.
Using the expression
argumentum ad
as a name for a type of
therefore somewhat misleading. Such argu-
ments are not fallacious simply because they
are based on ignorance. A more balanced view-
point is that they are typically based on partial
ignorance. Generally they are presumptive ar-
guments that can be used correctly and appro-
priately in some cases, yet can be misused in a
variety of ways in other cases. However, in some
cases, like case 2, they are negative epistemic ar-
guments based on knowledge that a particular
proposition is
in a given knowledge base.
Ignorance comes into it because the cases
of presumptive inference are characteristi-
cally based on ignorance (and hence are spe-
cies of arguments from ignorance) in two
First, they tend to be appropriately
used in a kind of case where knowledge-
based reasoning (hard evidence) cannot get
enough of a grip, or is not available within
the practical constraints needed to resolve a
problem or take prudent action. Second,
they involve a negative type of reasoning
based on exclusion.
Both the epistemic cases and the cases of
inconclusive presumptive reasoning charac-
teristically have a "negative logic," as used in
argumentation. The argument has the form:
A is not proven true (false), therefore A may
be presumed to be false (true). This "flip
flop" type of reasoning is, as shown above,
characteristic of how presumptive reasoning
functions in a context of dialogue by revers-
ing the roles (probative obligations) of the
proponent and respondent.
Because of this negative logic, it is still
worthwhile to preserve the name
tum ad ignorantiam in the logic textbooks as
a distinctive type of potentially erroneous or
fallacious argument to be on the lookout for,
because of its potential for misuse as a fal-
lacy. It is a distinctive type of argument that
can be used appropriately (correctly) in a
context of dialogue, in some cases, and inap-
propriately (incorrectly) in other cases.
The argument from ignorance is not exclu-
sively an inconclusive type of presumptive
argument, nor is it generally equivalent to
presumptive :
as a type of argumen-
tation. For it is also used in knowledge-based
(epistemic) reasoning. To the extent we
know a knowledge-based K is closed, i.e.
complete, in the sense of containing all the
relevant information, we can infer that if a
is not in it, then
is false. This
argumentation scheme for the
ad ignorantiam
has the following form.
All the true propositions in domain
knowledge are contained in
is in
is not in
For all
D, A
is either true or false.
is false.
This form of inference is deductively valid.
To the extent that it can be established (and
not merely presumed or assumed) that
closed, we can conclude on the basis of what
is known (and not just on the basis of pre-
sumption) that A is false. Hence, in such
(rare though they may be, in actual
practice), the
argumentum ad ignorantiam
not a merely presumptive type of argumen-
tation, in the sense of being inconclusive, as
opposed to being based on established
However, in many cases like case 1 and
case 4, the argument from ignorance is a rea-
sonable (nonfallacious) argument, but is a
weaker type of inference than a deductively
valid inference. It is a plausible or presump-
tive type of inference, in the sense of Rescher
(1976), which rests on a major premise that is
not strictly universal, but states how things
can be expected to go
(subject to exceptions
This type of pre-
sumptive inference is of a type to be identi-
fied or at least associated with the principle
of epistemic closure expressed by de Cornulier
(cited above). This second argumentation
scheme for the
argumentum ad ignorantiam
has the following form.
It has not been established that all the true
propositions in
are contained in
is a special type of proposition such that if
were true,
would normally or usually be ex-
pected to be in
is in
is not in
For all
is either true or false.
Therefore, it is plausible to presume that
false (subject to further investigations in
There may be various kinds of evidence that
back up the second premise for the use of
this type of inference. One is that
, if true,
would be a prominent item of knowledge in
a domain
, and would therefore normally
be expected to be included in any reasonably
comprehensive knowledge base in
this could vary, and would depend in a given
case how deep
with respect to
So conceived, the correctness of an argu-
ment from ignorance in a given case is best
evaluated by pragmatic criteria, i.e. relative
to a background context of dialogue or in-
quiry. In case 1, for example, an evaluation of
argumentum ad
needs to
take into account the matter of how far the
investigation into toxicity of this drug has
gone. In this context, the presumption of
nontoxicity for humans will carry a heavier
weight as the inquiry is more and more com-
plete. But as long as the findings are based
exclusively on tests with rodents, conclusions
drawn about toxicity for humans will remain
presumptive in nature. The correctness or in-
correctness of the
argumentum ad ig-
depend on what stage the
inquiry is in, and, if it is closed, what its find-
ings were. This in turn, depends on the stan-
dard or burden of proof appropriate for the
Not only is it right to say that the
tum ad ignorantiam
closely linked to pre-
sumptive reasoning and burden of proof
You could even say that the very structure of
argumentum ad ignorantiam
an expres-
sion of how presumptive reasoning and bur-
den of proof can function correctly in
argumentation to shift a presumption to the
other side in a dialogue. From a point of view
of this framework and criteria, the cases of
argument from ignorance found in ordinary
conversations and in the logic textbooks can, in
many instances, be shown to be
The University of Winnipeg
Received October 21, 1991
William Benoit, "Isocrates and Aristotle on Rhetoric,"
Rhetoric Society Quarterly,
vol. 20 (1990), pp. 251-60.
Allan Collins, Eleanor H. Warnock, Nelleke Aiello and Mark L. Miller, "Reasoning from Incomplete
Knowledge," in Daniel G. Bobrow and Allan Collins (eds.),
Representation and Understanding.
Studies in Cognitive Science
(New York: Academic Press,
1975), pp. 383-415.
Irving M. Copi and Carl Cohen,
Introduction to Logic,
8th ed. (New York: Macmillan, 1990).
"Knowing Whether, Knowing Who, and Epistemic Closure," in Michael Meyer
Questions and Questioning
Walter de
pp. 182-92.
Charles L. Hamblin,
Ray Reiter, "Nonmonotonic Reasoning,"
Annual Review of Computer Science, vol.
2 (1987), pp. 147-86.
Nicholas Rescher,
Plausible Reasoning
(Assen: Van
Frans H. van Eemeren and Rob Grootendorst,
Speech Acts in Argumentative
Foris Publications, 1984).
Douglas N. Walton,
Practical Reasoning: Goal-Driven, Knowledge-Based, Action-Guiding Argumenta-
(Savage, MD: Rowman and
John Woods and Douglas Walton, "The Fallacy of
Dialectica, vol.
32 (1978), pp. 87-99.
Reprinted in John Woods and Douglas Walton,
Fallacies: Selected Papers,
1972-1982 (Dordrecht:
pp. 161-73.
Work for this paper was supported by a Research Grant from the Social Sciences and Humanities
Research Council of Canada and a Fellowship from the Netherlands Institute for Advanced Study in
the Humanities and Social Sciences.
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... Woods and Walton would go on to characterize non-fallacious variants of most of the major informal fallacies, including circular or question-begging argument, the argument from ignorance, slippery slope, ad baculum, appeal to popular opinion, and ad verecundiam [34,35,36,37,38,39,40,41,42,45,46,47,48,49]. Fallacy theorists identified reasonable forms of these arguments in fields like law, economics, palaeontology, and ethics, not to mention more mundane contexts of everyday reasoning. ...
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As we reflect on the work of Douglas Walton, I want to encourage readers of this journal to look beyond the usual applications of logic and consider the domains of medicine and health. It is testimony to the intellectual breadth of Walton's ideas in argumentation theory and fallacies that his work should find a home in medical and health disciplines, particularly epidemiology and public health. In this paper, I examine three areas of Walton's theoretical approach to argument and fallacies that I have found most beneficial to my work on reasoning in public health. First, Walton's collaboration with John Woods resulted in a new, rigorous program of fallacy research. Integral to this new approach to the fallacies was the characterization of non-fallacious variants of most of the major informal fallacies. Second, Walton advocated for a third category of presumptive argument to sit alongside deduction and induction, with plausibility as the standard of rational evaluation. Many so-called informal fallacies, he contended, are rationally warranted presumptive arguments in the practically oriented contexts in which they are advanced. Third, Walton argued that presumptive arguments like the argument from expert opinion can be scrutinized using critical questions during systematic reasoning. They may also bypass critical questions and facilitate a quick leap to a conclusion based on one or two explicit premises during heuristic reasoning. Each of these three areas in Walton's work is discussed in the context of medicine and health, with illustration provided by the current Covid-19 pandemic.
... This argument is widely viewed as a fallacy because a lack of evidence or knowledge, it is claimed, cannot be used as grounds to accept a proposition as true (or false) (Krabbe 1995;Woods and Walton 1978;Walton 1995). However, in public health and other contexts (e.g., law), there are circumstances where this is not so clearly the case (Cummings 2002;2011;2015a;2015b;Walton 1992b). Imagine a scenario in which I want to establish whether guests at a wedding have been exposed to the salmonella bacterium in the food that is served to them at the event. ...
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The COVID-19 pandemic presents argumentation theorists with an opportunity to reflect on the ways in which people, agencies, and governments respond to the emergence of a new virus. Reponses have revealed a range of judgements and decisions, not all of which are rationally warranted. This article will examine errors in reasoning, several of which have reduced the public's compliance with important health measures. This article will also analyse rationally warranted reasoning about COVID-19 employed by public health agencies. In examining instances of good and bad reasoning during the COVID-19 pandemic, we can begin to construct a taxonomy of arguments that have facilitated and hindered individual and collective responses during this public health emergency.
... Looking at the record as a presence or absence proposition is not a viable interpretation of the archaeological record. Per the traditional aphorism "absence of evidence is not evidence of an absence," 41 arguing that only males were present based on the limited sample of male bison bones (and lack of female bison identified) in an archaeological context where most of the bones cannot be attributed to either sex due to preservation shortcomings is an uninformed and simplistic view of the processes that create the archaeological record. ...
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On the Ground •Bison have been a component of the Greater Yellowstone Area for more than 10,000 years. Archaeological sites are subjected to numerous natural and cultural factors that influence the preservation of organic materials. •The Yellowstone Plateau is a particularly challenging area for organic preservation due to acidic soils, bioturbation, sedimentation, and other pedogenic and geomorphic factors. •Our commentary presents a more complex understanding of the presence of bison in Yellowstone National Park and explains why using simple presence or absence of species is a flawed strategy and that a more sophisticated understanding of the archaeological record is necessary.
... Several philosophers attempted to vindicate inference from absence by pointing to circumstances under which it may be correct or at least plausible. Two lines of thoughts in this direction, independent but convergent in their main conclusions, were developed by Walton (1992Walton ( , 1996 and by Goldberg (2010Goldberg ( , 2011. 8 The main point in both these approaches is the following: Such inference is plausible if, or to amount that, the one making it is in the position to say (paraphrasing Goldberg, 2011) "If it were true, I would have had good evidence for it by now." ...
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Inferences from the absence of evidence to something are common in ordinary speech, but when used in scientific argumentations are usually considered deficient or outright false. Yet, as demonstrated here with the help of various examples, archaeologists frequently use inferences and reasoning from absence, often allowing it a status on par with inferences from tangible evidence. This discrepancy has not been examined so far. The article analyses it drawing on philosophical discussions concerning the validity of inference from absence, using probabilistic models that were originally developed to show that such inferences are weak and inconclusive. The analysis reveals that inference from absence can indeed be justified in many important situations of archaeological research, such as excavations carried out to explore the past existence and time-span of sedentary human habitation. The justification is closely related to the fact that archaeology explores the human past via its material remains. The same analysis points to instances where inference from absence can have comparable validity in other historical sciences, and to research questions in which archaeological inference from absence will be problematic or totally unwarranted.
Despite the importance the army had throughout the history of the Roman Empire, and despite the vivid images that immediately come to mind when we think of the legions of Rome, many aspects related to the organizations of the armed forces under the rule of the emperors remain arguably obscure: the production of weapons and armours for Roman soldiers is among them. Aiming to develop a strong theoretical approach for the analysis of this particular aspect of ancient military logistics, this thesis analyses the situation in the Roman province of Dacia (AD 106-AD 270).The conceptual basis and development of Roman military logistics is studied through the combined use of archaeological data, literary sources, and epigraphy. The pattern of military sites, mines, and administrative centres of the ancient province of Dacia is therefore interpreted as the framework in which a complex and multi-layered productive system was implemented and developed.
Classical models predominantly approach persuasion qualitatively or descriptively. In the past couple of decades, researchers have explored quantitative and predictive models to describe how people integrate new evidence within their pre-existing beliefs. The so-called Bayesian models take point of departure in people’s subjective view of the world to predict how they will integrate new information. The predictive capacities of these models highlight the possibility of generating process-oriented mathematical models that can capture individual differences and predict people’s belief revisions. This chapter shows how formal models can capture subjective rationality.
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By explaining the argument from ignorance in terms of the presumption of innocence, many textbooks in argumentation theory suggest that some arguments from ignorance might share essential features with some types of presumptive reasoning. The stronger version of this view, suggesting that arguments from ignorance and presumptive reasoning are almost indistinguishable, is occasionally proposed by Douglas Walton. This paper explores the nature and limits of the stronger proposal and argues that initial presumptions and arguments from ignorance are not closely connected. There are three main reasons. First, the argument from ignorance, unlike typical presumptive reasoning, is a negative kind of inference. Second, the typical initial presumption is sensitive to a broader set of defeaters and thus assumes a higher (negative) standard of acceptability. Third, in dialectical terms, initial presumption and argument from ignorance bring different attacking rights and obligations. I conclude that Waltonian intuition is unsupported or, at best, is limited only to practical presumptions and practical arguments from ignorance.
Reasoning from Incomplete Knowledge Representation and Understanding
  • Allan Collins
  • Eleanor H Warnock
  • Nelleke Aiello
  • Mark L Miller
Allan Collins, Eleanor H. Warnock, Nelleke Aiello and Mark L. Miller, "Reasoning from Incomplete Knowledge," in Daniel G. Bobrow and Allan Collins (eds.), Representation and Understanding. Studies in Cognitive Science (New York: Academic Press, 1975), pp. 383-415. NONFALLACIOUS ARGUMENTS FROM IGNORANCE / 387
Practical Reasoning: Goal-Driven, Knowledge-Based, Action-Guiding Argumentation
  • Douglas N Walton
Douglas N. Walton, Practical Reasoning: Goal-Driven, Knowledge-Based, Action-Guiding Argumentation (Savage, MD: Rowman and Littlefield,1990).
  • Charles L Hamblin
Charles L. Hamblin, Fallacies (London: Metheun,1970).