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Res Eng Des (t992) 4:13-22
Research in Engineering Design
Theory, Applications, and
Concurrent Engineering
@ 1992 Springer-Vedag New York Inc.
Engineering from Reflective Practice
D.I. Blockley
Department of Civil Engineering, University of Bristol, Bristol, UK
Abstract.
Some ideas for a new epistemology, encom-
passing practical action, based on the concept of reflec-
tive practice, are presented. The term reflective practi-
tioner was first suggested by Schon (1983) in an analysis
of the need to define the nature of practical competence.
The prevailing culture of technical rationality, which de-
pends on science for it rigor, is compared with that of the
"wise engineer" promoted by Elms (1989). Worldview,
quality, systems thinking, and responsibility are dis-
cussed as preliminaries to an analysis of reflective prac-
tice. The model is based on the passing of hierarchically
structured sets of message patterns from perception to
reflection to action. Intelligence is defined as an ability to
construct, evaluate, and act on alternative scenarios of
the future in the reflective phase. Design involves the
construction of scenarios where imagined artifacts oper-
ate to achieve predefined needs for some defined per-
son(s). Rigor for the reflective practitioner stems from the
achieving of appropriate objectives. The similarities and
differences between science and engineering become ap-
parent when both are viewed as examples of reflective
practice.
1 Introduction
In order to understand better the nature of engineer-
ing design I will argue that there is a need for a new
epistemology of practical action. Some preliminary
ideas are presented based on the idea of "reflective
practice". Culture will have an underlying role. By
culture I mean the systems of agreed upon mean-
ings that serve as recipes, or guidelines, for behav-
ior in any particular society. An "agreed upon"
meaning is equivalent to a symbol since a symbol is
something the meaning of which is bestowed upon it
by those who use it (Barrett t991). Symbols, in the
form of words or Sounds of natural or formal lan-
guages, are the means through which we express
knowledge. It is clear therefore that knowledge is
Offprint request: Department of Civil Engineering, Univer-
sity of Bristol, Bristol BS8 1TR, UK
not value-free nor is it ever complete (Blockley
1989).
Engineers when using their professional knowl-
edge are therefore faced with value judgements.
They take responsibility for decisions, but what can
society expect of them? I will argue that the ideas of
systems engineering currently form the best ap-
proach to engineering design.
2 Reflective Practice
The term reflective practice was first introduced by
Schon (1983) in a discussion concerning the role of
professionals and the need to define the nature of
practical competence. He was concerned with
questions such as: What is the prevailing culture of
the professions? To what extent is there rigor in
professional practice? Why is it that professionals
often seem to know more than they can articulate
(i.e., have tacit knowledge)? Is there a crisis of con-
fidence in the professions?
So to what extent is there rigor in professional
practice? In modern times the culture of most pro-
fessions is largely formed through the education and
training their practitioners receive at university.
Schon pointed out that universities are, for the most
part, committed to a particular epistemology which
he called "technical rationality." This he defined as
instrumental problem solving made rigorous by the
application of scientific theory and technique. He
maintained that the professions have paid a heavy
intellectual price for being successfully incorpo-
rated, over the last century, into the universities.
He quotes Thorsten Veblen (1918)
"The universities have a higher mission to 'fit men for a
life of science and scholarship; and they are accordingly
concerned with such discipline only as they will give effi-
ciency in the pursuit of knowledge' whereas the lower
schools are occupied with 'instilling such knowledge and
habits as will make their pupils fit citizens of the world in
whatever position in the fabric of workday life they may
fall."
t4 BIockley: Engineering from Reflective Practice
Technical rationality is embedded in our institu-
tional context, it governs our understanding of the
relationship between research and practice, it forms
the norms of the curriculum of professional educa-
tion. By this culture researchers are supposed to
supply the basic and applied science from which the
techniques for practical problem solving are de-
rived. The researchers' role is therefore considered
to be superior because it is perceived as being more
rigorous. The rule is that rigorous basic and applied
science comes first, followed secondly by the tess
rigorous skills required to apply that knowledge to
real world practice. Notice that these skills are con-
sidered secondary, in fact there is often an implica-
tion that they are not knowledge at all.
So what is the problem with our present culture?
Schon maintains that there is a crisis of confidence
in the professions. Consider three examples where
the trust of lay people in experts has been damaged.
Firstly, there have been financial scandals where
people in the city have used their specialist knowl-
edge and positions for personal gain; that is per-
ceived as a question of ethics. Secondly, there have
been a number of technological disasters, such as
Three Mile Island and the Challenger, which illus-
trate that even technical experts can get things
wrong; that is perceived as a question' of technical
competence. Thirdly, almost everyday the newspa-
pers report disagreements between experts about
the causes of some difficult phenomena, such as the
causes of heart disease or food poisoning. In court
expert witnesses disagree about technical issues,
for example, concerning the effects of environmen-
tal pollution; these are perceived as questions con-
cerning the limits to the extent of our knowledge. In
a culture where science is supposed to provide all of
the answers, the iayperson can be forgiven for being
rather confused and for losing confidence in the pro-
fessionals.
A consequence is that there is now an increased
questioning of the rights and freedoms of profes-
sionals. Their license to determine who shall be al-
lowed to practice is rooted in deeper questions of
professional claims to have "extraordinary knowl-
edge" and this depends on our understanding of the
nature of knowledge and its relationship with practi-
cal competence.
Practitioners know more than they can articu-
late, this has been called tacit knowledge (Polanyi
1958). Schon attempted to analyze the capacity that
practitioners often reveal, of being able to reflect
through intuitive knowing and of using this capacity
to cope with unique, uncertain, and conflicting situ-
ations. Later in the paper an alternative conceptual
framework for this will be presented.
Science, it is often argued, is objective and value-
free. By contrast practitioners are frequently em-
broiled in conflicts of values, goals, purposes, and
interests. For example, a central difficulty in engi-
neering design is the balance between safety and
cost. Thus, any consideration of practical action
must face up to the need to define a value system.
Schon also identified the need to recognize that pro-
fessionals deal not just with problems but rather
with problem situations. He argued that complex
systems are sets of interacting problems that he
called "messes." He maintained that professionals
do not solve problems they manage "messes." The
failure of the algorithmic approaches to practical
problem-solving, as for example in Operational Re-
search, is because such approaches fail to help with
the formulation of problems from out of the
"mess." The scientific approach is to isolate parts
of a problem "mess" by selective inattention until a
clear statement of a difficulty can be addressed rig-
orously. This provides a major dilemma for the pro-
fessional because the selective inattention of the
scientist may in fact have excluded important as-
pects of the original problem that cannot be ignored.
The professional then relies on what Schon defines
as "reflection in action"wthe kind of knowing in-
herent in intelligent action. Skillful action depends
upon more than the practitioner can articulate. The
question then is whether these skills are in any
sense inferior to the rigor of the scientific approach.
The model of reflective practice to be presented will
shed light on this question.
3 Wisdom Engineering?
Elms (1989) has argued that engineering education
tends, for the most part, to concentrate on the giv-
ing of knowledge (rather like the pouring of water
into a jug!). He argued that knowledge alone does
not give capability. An engineer must necessarily be
technically competent and clearly knowledge is part
of that. However, there are people with a great deal
of knowledge but who are not good engineers. Ca-
pability is something more stable, more endurable
than knowledge, but which tends to be acquired al-
most incidentally as a byproduct of obtaining
knowledge. Design courses perhaps are an excep-
tion as they particularly involve more than a trans-
fer of knowledge. However, many people have ar-
gued that these skills cannot (should not) be taught
in a University since they rely on personal skills and
require the incentive of real responsibility. Elms ar-
gues that one of the most fundamental reasons why
engineering capability is not taught is that the very
Blockley: Engineering from Reflective Practice 15
nature of engineering is poorly understood. He sees
it as fundamentally different from science, since sci-
ence is truth-oriented and engineering is goal-ori-
ented. Science uses words such as true/false
whereas engineers are concerned with the quality of
a solution such as "good," "bad," "better,"
"worse." Engineering researchers are more likely
to be involved with "how" to do something rather
than whether something is true or false. At a very
fundamental level the very discipline of philosophy
is concerned with knowledge and its methodology is
aligned with mathematics and science and that per-
haps is why it is inappropriate for engineering. Elms
quotes Maxwell (1984), who was concerned with
what he saw as the basic flaw in the scientific
method which is that it deals only with what is true/
false and appears not to care about the use of
knowledge for good or ill. Such a lack has obvious
ethical implications and may indeed be a major
cause of some of the major ills of the world. Max-
well argued that scientific knowledge was being
neither produced nor used responsibly if it were
regarded as being independent of any values.
Maxwell proposed a philosophy of wisdom which is
a combination of knowledge and values.
Elms argues that wisdom is more than a matter of
action and good decision-making. Rather it is a
quality of the way of looking at things; it is the
ability to see the world clearly in a coherent picture.
This clarity is simple but not simplistic and depends
upon strong underlying conceptual models of the
world. Elms sums up his ideas as follows: "a wise
person has to have knowledge, ethicalness and ap-
propriate skills to a high degree. There also has to
be an appropriate attitude; an ability to cut through
complexity and to see the goals, the aims, the fun-
damental essentials in a problem situation, and to
have the will and purpose to keep these clearly in
focus. It is to do with finding simplicity in complex-
ity. More fundamentally it is to do with world views
and the way wise persons construct the world in
which they operate; which is to say, in engineering,
that wisdom is to do with having appropriate con-
ceptual models to fit the situation."
4 Incompleteness
Is there a dilemma of a choice between rigor and
relevance, the resolution of which requires the
skills of a wise engineer? In the search for improve-
ment by introducing some' rigor, the practitioners
"mess" can be analyzed and particular difficulties
cut down to manageable proportions by a process of
selective inattention as mentioned earlier. This sci-
entific approach is reductionist, it selects only part
of the totality for consideration. Of course this ap-
proach has been spectacularly successful, the
whole history of physical science has been built
upon it, but nevertheless it must not be confused
with the difficulties of dealing with the original
"mess." In fact it has been singularly unsuccessful
in dealing with the social sciences where the prob-
lems are distinctly more "messy." Certainly the as-
sumption should be challenged that science should
be considered to be a superior exercise simply be-
cause it is more rigorous. It is in fact, often a sim-
pler (but not simple) execise because the number of
interactions in the problem set are much reduced.
The central problem in the dilemma is that although
the process of selective inattention may result in
sets of simpler problems which can be tackled rigor-
ously, each one may be so unlike the original
"mess" that they are barely relevant. There is
therefore indeed a dilemma of rigor or relevance for
the practitioner and the resolution of the dilemma
requires wise counsel. However, the dilemma is
only a dilemma in terms of the search for truth. The
rigor in practical problem-solving is obtained
through the determination to achieve objectives and
this can be just as intellectually challenging.
But even when a problem has been sharply de-
fined and solved scientifically there are still funda-
mental problems of incompleteness. The population
of possible future events is infinite, since as Plato
noted, "How can we know what we do not know?"
The problems of the incompleteness of scientific
and mathematical knowledge and its relationship
with engineering have been discussed previously
(Blockley 1980, 1989). The theorems of Godel de-
fine the limits to mathematics, the Uncertainty Prin-
ciple defines the limits to physics, and the recent
discoveries of deterministic chaos demonstrate that
even simple systems can behave in a complex man-
ner. Two kinds of models have been distinguished.
The first is a closed world model which represents
total knowledge about a problem and in which every
thing is true or false and no undefined or inconsis-
tent states are possible. In a closed world the infor-
mation is complete in that all and only the relation-
ships that can possibly hold among the concepts are
those implied by the given information. The models
of classical science are of the closed world type. In
an open world a concept may be true, false, un-
known, or inconsistent with all degrees of uncer-
tainty in between; these, of course, are the real
world problems of engineering. In the world of tech-
nical rationality inconsistencies are forbidden.
However, in practical problems the finding and set-
16 Blockley: Engineering from Reflective Practice
tling of inconsistencies is an important element in
the problem formulation and solution process.
5 Need for Theory of Practical Competence
Thus, there is a need for an epistemology which
encompasses practical action. Such a theory should
not "throw the baby out with the bathwater" and
reject the philosophy of technical rationality but
rather it should unify it with practical action. In
other words a theory of practical action should en-
compass "pure," "applied," and "practical" ap-
proaches; it should cover both the closing down,
judgmental skills of analysis, and the opening out,
creative skills of synthesis. The theory should de-
velop new ideas about intellectual thought and prac-
tice. The ideas presented here are an attempt to
begin the search for such a unifying theory. We
begin with some preliminaries which examine how
each of us "sees" the world, what we are trying to
achieve, how we approach problem-solving rigor-
ously, and how we handle the consequences of our
actions.
6 Some Preliminaries
6.1 Worldview
Everything that we think and do depends upon our
point of view, it depends upon the way in which we
look at the world. In philosophy this is called the
"Weltanschauung" (Avison and Fitzgerald 1988).
We attribute meaning to something by interpreting
it in the light of our experience and education. How-
ever, as social anthropologists would point out and
as discussed above, our worldview is also formed
through the culture of the society in which we live.
Within our western culture, however, the same is-
sue will tend to be formulated, for example, as an
economic problem by an economist, as a technical
problem by an engineer, and as an organizational
problem by a sociologist. Each wortdview may be
valid in that it may be internally consistent and that
propositions deduced from it may correspond with
the perceived facts.
In considering how these worldviews are
formed, it is useful to have some sort of model of
the processes of the brain which we can character-
ize as follows. When we perceive something, a set
of messages are sent to the brain from our sense
organs. The mind organizes these messages into
patterns, the nature of which need not concern us
directly for this purpose, and these patterns form
the software of our brains. A simple model of recog-
nition is that all that is required is a strong enough
message to trigger an existing pattern and the mind
then follows it. The purpose of thinking is to find
patterns and, of course, it is possible to lock into the
wrong pattern. Learning is the relating of new pat-
terns to existing patterns. Creativity is the linking of
patterns not previously linked. Some patterns may
be genetically inherited and therefore part of the
"hardware," the patterns we share with our par-
ents. A large repertoire of patterns derives from a
rich set of experiences and thinking is then much
more powerful. A danger is that a small set of pat-
terns results in intolerance and a lack of imagina-
tion. Two people will tend to share the same world-
view if they come from similar cultural, social, and
educational backgrounds. In summary, we can
imagine a person's worldview as a set of patterns
laid down in the brain.
6.2 Quality
The objective of a reflective practitioner is to pro-
duce "something" with specific qualities. The
"something" will have an objective existence, such
as the expression of a theory in natural or formal
language or it could be a physical artifact such as a
bridge. However, the meaning of that objective ex-
istence, the interpretation of that existence, will de-
pend on the person's worldview expressed in terms
of qualities.
The word quality has at least two meanings. The
first is as a degree of excellence and the second is as
a trait or characteristic. The reflective practitioner
is interested in setting and reaching goals. The qual-
ity of excellence is achieved through the setting and
achieving of difficult goals. The idea that excellence
can only be achieved through the search for truth is
partial, since it is only the case when that is indeed
the goal (as for example is usually understood to be
the purpose of academic research). The concept of
"appropriateness" is more important than truth
since many objectives may be reached without
knowing, or being centrally concerned with, what is
actually true. Of course the reflective practitioner is
interested in truth but his or her objective is to set
"appropriate goals" and to be rigorous in his or her
determination to achieve them.
The goals are defined in terms of appropriate lev-
els of attainment of required traits or qualities. The
more easily measurable are the goals, the more eas-
ily it is determinable that they have been reached.
Thus, the rigor of science and technical rationality
is included in this analysis if truth is the goal--but
other goals may be more appropriate in other situa-
tions.
Blockley: Engineering from Reflective Practice 17
6.3 Systems
"Systems" is a modish word, but what does it actu-
ally mean? It really is itself a subject in which one
can think and talk about other subjects, it is a meta-
discipline whose subject matter can come from vir-
tually any other discipline. Thus, it is more of an
approach than a topic; a way of going about tackling
a problem. In simple terms a systems approach is
one which takes a broad view, which tries to take
into account all aspects and which concentrates on
the interactions between different parts of the prob-
lem. The scientific approach characterizes the
world by assuming that natural phenomena are or-
dered, regular, and not capricious and it is reduc-
tionist so that problems are broken down into their
constituent parts and tackled. Systems thinking al-
ternatively questions the assumption that the com-
ponent parts are the same when separated out as
when they are part of the whole. For more discus-
sion of the systems approach see Checkland (1981).
It is obvious that whole systems have character-
istics that the subsystems do not have. For exam-
ple, a human being is made up of subsystems (ner-
vous system, skeleton, etc.) and none of them are
able to walk about for that is a characteristic of the
human being. The term holon was coined by Koes-
tler (1967) to describe the idea of something which
is both a whole and a part. Thus, a human is a holon
in that a human is a whole (with a set of subsystems)
and a part (of a higher order systems, such as family
and other societal groupings).
The reflective practitioner is, in the terms of
Elms, a wise engineer and a systems thinker.
6.4 Responsibility
The concept of responsibility is central to the role of
the reflective practitioner. The RP is aware of the
limitations of his knowledge and skills and is very
much aware also of the duties owed both to clients
and to the general public. Thus the RP is not con-
cerned principally with the degree of truth of a the-
ory or model, rather the RP is concerned with the
taking of responsibility to act on the basis of the
theory or model. The taking of responsibility im--
plies not that one has earned the right to be right or
nearly right but that one has taken precautions that
one can reasonably be expected to take against be-
ing wrong (Blocktey 1985).
7. The Model of Reflectiqe Practice
We will represent all human activities in terms of a
hierarchically structured set of evolutionary prob-
Fig. 1. The reflective practice loop.
lem-sotving processes. In overview the problem-
solving loop is simply this: we perceive the state of
the world (the senses) as sets of patterns in the brain
(these patterns may be chemical, electrical, biologi-
cal, etc., it matters not for the purposes of this dis-
cussion), we interpret our perceptions (think/re-
flect), we act upon the world (behave), and finally
we perceive a new state of the world.
The RP loop is (Fig. 1):
world --~ sense ~ think (mind) --~ act ~ world
In other words:
world ~ perception --~ reflection --~ action ~ world
Needs are patterns which may be in-built or
learned. Problems are the result of mismatching
patterns. The world changes through our actions,
we have a new set of perceptions and the loop is
repeated. Our attention is the focus of our percep-
tion and is controlled by the very processes of a
hierarchically structured set of problem-solving
loops at differing levels of definition (see Fig. 2) all
occurring in parallel.
In mathematical terms, mind is a many-to-many
functional mapping from perception to action. We
can imagine this mapping as a relation which could
be a set of functions or a set of rules.
t
_.~_-
ou~.
Ea
E~
=~
Time
t8 Blocktey: Engineering from Reflective Practice
Physical World
Key : multiple communication
channel (parallel)
Perception
(~) Reflection
Action
Fig. 2. Hierarchically structured reflective practice loops.
In our subconscious mind this mapping from sen-
sory perception to action is determined but not nec-
essarily determinate. Some of these mappings de-
fine skills which may be innate (e.g., musical) and
some which are learned (e.g., playing a piano). The
mind receives signals from sense organs and sends
out signals to various parts of our body. For exam-
ple our body temperature control mechanism is of
this type. Language is the result of linkages be-
tween patterns of perceptions and patterns of audi-
ble sounds (phonemes) and visible marks or sym-
bols (marks such as numbers, letters). These
linkages are themselves patterns.
Learning is the development of new patterns and
new linkages between patterns. It is an evolutionary
problem-solving process central to the building of
the mind. We can postulate that clusters of patterns
can be linked to word patterns to form higher level,
more general words or concepts. We can imagine
these concepts are linked hierarchically. Linkages
between higher level concepts may also be clus-
tered to form relationships.
Mental models are patterns representing con-
cepts and relations.
Language is learned from the base of the subcon-
scious mind by a learning process. Our conscious
mind is the result of the formation of mental models
expressed in terms of language. Through language
we can express ideas about ourselves (identity) and
about our own knowledge (high-level reflection).
Through language we reflect and act on the world in
a conscious evolutionary learning problem-solving
process.
Memories are patterns in the mind and through
those which are stored in our conscious mind we
have concepts of time and identity~ Imagination and
creative thinking is the result of forming links be-
tween memory patterns which were not previously
linked. Scenarios are temporally ordered sequences
of events. Through imagination we can build sce-
narios which have not actually happened both about
the past and about the future. Note however that
these links are made between existing patterns in
the mind. The richness of alternative future sce-
narios must therefore depend on the richness of
past experience.
Knowledge is a set of mental models. Some men-
tal models cannot be expressed in natural or formal
language and these are part of, but do not define,
the subconscious mind (e.g., the rules controlling
heart beat). Mental models that can be expressed in
natural or formal language are part of, but do not
define, the conscious mind. Some models can be
subconscious some of the time and conscious at
other time (e.g., learned skills such as driving), and
some are almost entirely conscious (e.g., speech).
Conscious problem-solving is an evolutionary pro-
cess where actions are taken on the basis of an eval-
uation of alternative scenarios, which is reflection.
Evolution derives from learning.
Blockley: Engineering from Reflective Practice 19
Consciousness is attributed to an organism when
it shows intelligence. I define intelligence as an abil-
ity to construct, evaluate, and act on alternative
scenarios of the future. The richer the ability to
construct scenarios the more intelligent we suppose
the organism. Notice that by this definition intelli-
gence also includes action.
Penrose (1990) quotes Konrad Lorentz describ-
ing a chimpanzee in a room which contains a ba-
nana suspended from the ceiling just out of reach,
and a box elsewhere in the room: "The matter gave
him no peace, and he returned to it again. Then
suddenly--and there is no other way to describe
it--his previously gloomy face 'lit up'. His eyes
now moved from the banana to the empty space
beneath it on the ground, from this to the box, then
back to the space, and from there to the banana.
The next moment he gave a cry of joy, and somer-
saulted over to the box in sheer high spirits. Com-
pletely assured of his success, he pushed the box
below the banana. No man watching him could
doubt the existence of a genuine 'aha' experience in
anthropoid apes."
The conscious mind has the ability to build sce-
narios, hence to make choices to best satisfy needs
in a set of reflective practice loops. Thus, by this
interpretation, the chimpanzee is indeed in posses-
sion of a conscious mind. However, the mind is
primitive and is unable to form the patterns neces-
sary for written or spoken language, although some
animals are able to use sign languge. Thus, a central
characteristic of intelligence is the ability to con-
struct scenarios which include the use of tools to
manipulate objects in the world. It involves the abil-
ity to construct scenarios in which artifacts already
in the world are manipulated to enable the organism
to achieve its needs (such as food in the case of the
chimpanzee).
The next level of intelligent behavior is the ability
to make a tool or artifact. This is accomplished by
perceiving the world, imagining alternative sce-
narios, and evaluating and choosing one of them
(i.e., design) and then taking action to change the
world (i.e., manufacture) so that the chosen sce-
nario is realized. At this level the chimpanzee
would have in some way to see that the box must be
altered before it is suitable for standing on to reach
the banana. Further, at an even higher level, the
chimpanzee would have to be able to conceive the
nature of the box and be able to manufacture it from
some available timber.
Tools are artifacts which extend the capabilities
of human beings and the 'whole of our activity is
based on this ability. Human beings are compara-
tively weak, compared with some other animals,
when faced with dealing with the natural world
without the use of tools. Thus to fulfill a basic need
such as food, early man used primitive tools. As
men were able to satisfy basic needs, higher level
needs (as expressed for example by Maslow's hier-
archy of needs) became important too. In the mod-
ern western world people pursue top-level goals,
such as self-actualization, because the basic needs,
such as food and safety, are relatively easily satis-
fied.
The need to explain and understand our world is
also a high-level need. In the history of human de-
velopment as our understanding has increased so
we have been able to develop more sophisticated
tools. Thus, the evolution of science has been inti-
mately bound up with practical action. As a simple
example the tool most basic to science is a rule for
measuring length; of course measurement is the ba-
sis of the physical sciences. The history of science
and engineering are therefore intimately interwoven
and interconnected. Better tools mean more under-
standing which in turn enables the production of
better tools. Modern tools are complex systems of
artifacts, such as computers, but also include cars
and airplanes, buildings, and power stations; in fact
all products of practical endeavor (i.e., engineer-
ing). Modern nuclear physics, for example, is en-
tirely dependent on the engineering of vast particle
accelerators. Although engineers apply science
they are not applied scientists;just as scientists use
engineering but are not "pure engineers."
It is clear that design is central to human activity.
Design is the construction of scenarios where imag-
ined artifacts operate to achieve predefined needs
for some defined person(s). It is limited only by the
imagination of the designer. It involves the creative
linkage of patterns of concepts to form new rela-
tionships. It involves the analytical, judgemental
evaluation of these creations against clear criteria.
Thus, the reflection phase in the model of the
reflective practitioner becomes increasingly sophis-
ticated as we move from the use of tools through to
the design and manufacture of tools, which is engi-
neering.
8 Problem-Solving
The usual characterization of the problem-solving
loop is of the form
problem -+ collect information -+ find alternative solu-
tions -+ evaluate alternatives -~ select an alternative -+
implement solution --+ follow up consequences -+ review
situation -+ new problem.
20 Blockley: Engineering from Reflective Practice
In terms of the model of reflective practice this
characterization is a partial high-level model. All
aspects of this characterization are included in the
reflective practice model of Fig. 1. The first part is
contained in the reflective phase, the implementa-
tion phase corresponds to action, and the follow-up
consequences and review are themselves lower
level reflective practice loops. The importance of
perception and hence worldview is not captured
and the essential integration of perception, reflec-
tion, and action missed.
9 Science and Engineering
In order to clarify further the interpretation of pro-
fessional activities using the reflective practice
model, we can now examine the relationship be-
tween science and engineering in terms of the
model. The first step is to clarify objectives. What
needs are being fulfilled? The objective of science is
to produce knowledge which has specific qualities
(truth, explanation, prediction, etc.). The need is to
understand.
The objective of engineering is to produce arti-
facts which have specific qualities (safety, function,
form, etc.). The need is to operate on the world,
which in turn may be driven by several needs, for
example, to feed, to protect personal safety, to un-
derstand. Table 1 is an attempt to capture and com-
pare the qualities of engineering and science. The
qualities are grouped into the central headings of
function, form, grounding, specification, etc. The
qualities in the first and third columns are those
usually listed in discussions of these matters. No-
tice however that they are not mutually exclusive.
For example, a scientific theory may be fit for its
purpose if the purpose is to predict and explain.
Similarly, a scientific theory will be appropriate if
being appropriate in science means being precise
and clear.
Perhaps the most difficult comparison in Table 1
is that concerning the quality of "grounding."
Clearly, science is grounded on truth, the whole
basis of science is the search for truth. (Here I use
the correspondence theory of truth, see Table 2.)
However, the concept of a true artifact is meaning-
less; engineers are interested in truth only to the
extent that it enables them to produce artifacts that
have the requisite qualities. The hypothesis pre-
sented here is that an artifact is grounded on safety.
Table 2 presents some comparative definitions of
terms in science and engineering. The term calcula-
tion procedure model was coined by Blocktey and
Henderson (1980) in an attempt to capture the com-
Table
1. A categorization of the qualities of scientific and
engineering knowledge
Scientific Engineering
knowledge Quality knowledge
Prediction <--- Function ---, Fitness for
Explanation purpose
Simplicity ~ Form ~ Environmental
Elegance Economy impact, beauty
cost
Truth content ~ Grounding --~ Safety content
Consistency
Precision <--- Specification --+ Appropriateness
Clarity
Abstraction <-- Applicability --+ Relevance
Domain width Practicality
Relevance
Information *-- Grounding & ---, Hazard
Content specification Content
Analysis ~ Mode ~ Synthesis
Design
Hypotheses ~ Expression ~ Calculation
Propositions Procedure models
plex conjunction of various engineering models that
are put together to form a design procedure. The
analogy between truth and safety is carried through
into analogous definitions of "degree of truth" and
"safety margin," of "truth content" and "safety
content, of "information content" and "hazard
content."
It must be stressed that it is not being suggested
that engineers are only concerned with the right-
hand column of Table 2, or indeed that scientists are
only concerned with the left-hand column. The dis-
tinction being sought is that engineers apply science
but are not "applied" scientists, just as scientists
design experiments but are not "pure" engineers.
The language of engineers is distinct but analogous
to that of scientists. The thesis is that both engi-
neers and scientists are reflective practitioners--
they are evolutionary problem-solvers--the differ-
ence is in the nature of the problems they are trying
to solve.
10 Closure
In this characterization of reflective practitioners as
problem-formers and -solvers, there are two ex-
tremes and caricatures. At one end is the muse, the
thinker who thinks so deeply that he or she is para-
lyzed into inaction by prevarication. At the other is
the unthinking practitioner, the automaton, who
does not know why he or she does what he or she
does--everything is done by rote. In the actual
world, where the problems we face as a human
Blockley: Engineering from Reflective Practice 21
Table 2. Some comparative definitions for science and engineering (continued on following page)
Scientific Engineering
knowledge knowledge
Expression
Hypotheses (theories, models) from which we deduce
propositions. They result from our need to understand the
world.
Truth of a proposition
Correspondence between the state of the world as de-
scribed by a proposition and the actual state of the world.
Test of a proposition
The establishment of the truth of the proposition through
experiment, usually in a closed world.
Appropriateness
Of a hypothesis (proposition) the degree to which a hy-
pothesis (proposition) may be treated as if it were true.
Falsity of a proposition
Lack of correspondence between the state of the world as
described by a proposition and the actual state of the
world.
"Degree of truth" of a proposition
The "distance" between the state of the world as de-
scribed by a proposition and the actual state of the world.
Logical probability of a proposition
A measure of the degree of truth of the proposition
Truth (falsity) content of an hypothesis (proposition)
The relative number of true, consistent (false, inconsistent)
propositions which may be deduced from an hypothesis
(are consequent on a proposition).
Possibilities
Possible states of the world.
Precision of a proposition
The extent to which possibilities are excluded.
Clarity of a proposition
The ease with which a state may be identified.
Evidence for an hypothesis (proposition)
The demonstrated truth content of the hypothesis (proposi-
tion).
information content of a proposition (hypothesis)
The extent to which a proposition (hypothesis) has precise
clear truth content.
Knowledge
A set of hypotheses (propositions) which have high truth
and/or high information content.
Closed world model
Total knowledge about a system everything is true or
false. Models based on selective inattention, some possibil-
ities can be ignored.
Expression
Calculation procedural models (cpms) from which we
design and build artifacts. They result from our need to
operate on the world.
Safety of an artifact
Correspondence between a required state of the world and
the actual state of the world.
Test of an artifact
The establishment of safety of the artifact by nature, as a
cunning adversary and by human operation in an open
world.
Appropriateness
Of a cpm (artifact) the degree to which the cpm (artifact) is
fit for its purpose.
A required (unacceptable) state of the world for an artifact
A state such that the artifact is fit (is not fit) for its pur-
pose.
Failure of an artifact
Lack of correspondence between a required state of the
world and the actual state of the world.
Safety margin of an artifact
The "distance" between the required state of the world
and the actual state of the world.
Reliability of an artifact
A measure of the safety margin on the artifact.
Safety (failure) content of a cpm
The relative number of safe, consistent (failed, inconsis-
tent) states of the world which may be deduced from a
cpm.
Scenarios
An ordered set of possibilities.
Appropriateness of a epm
The fitness of the cpm for its purpose.
Hazard content of an artifact (cpm)
The extent to which an artifact (cpm) has precise clear
failure content.
Proneness to failure of an artifact
A measure of the hazard content of the artifact.
Limit state boundary of an artifact for a given scenario
The boundary between required and unacceptable states of
the world for the artifact.
Safe scenario of an artifact
A scenario in which all of the states are safe.
Failure scenario of an artifact
A scenario in which the final state is a failure.
Knowledge
A set of cpms (artifacts) which have high safety and small
hazard content.
Open world model
Partial knowledge about a system some things are true,
some false, some are unknown, and some are inconsistent.
No possibilities can be ignored.
Risk for an artifact in a given state
The reliability of the artifact in that state and the conse-
quences of failure.
22 Blockley: Engineering from Reflective Practice
Table 2. (Continued from previous page)
Scientific Engineering
knowledge knowledge
Values
Can largely be ignored.
Technical rationality
Problem-solving made rigorous by the application of scien-
tific theory and technique.
Risk content for an artifact in a given scenario
The combined risks for all of the states of the world in the
scenario.
Risk content of an artifact
The totality of risk content for all failure scenarios.
Robustness of an artifact
The negation of the risk content.
The dependability of a hypothesis (proposition)for a Deci-
sion
The information content and relevance of an hypothesis
(proposition)
Values
Cannot be ignored.
Design
Changing existing situations into preferred ones.
Practical competence
The quality of producing artifacts of appropriate qualities.
Reflective practice
The thoughtful achievement of practical competence.
Research in practice.
race, seem to get progressively more difficult, it is a
question of balance. In the spectrum of problem-
solvers, from philosopher to roadsweeper, every-
ones' contribution is important. To obtain quality it
is suggested that the most effective means for im-
provement is to think in a systems manner. Table 3
sets out a comparison between the systems view of
the reflective practitioner and the scientific view of
the technical rationalist. In the final analysis, we
hope that people will work together to appreciate
each other's worldview, to improve communica-
tions and teamwork, to set personal and corporate
Table 3. Reflective practice versus technical
rationality
Reflective practice Technical rationality
Systems Selective inattention
Synthesis Analysis
Quality Truth
Parallel Sequential
Hierarchical Flat
Nonlinear Linear
Social/technical Separate
Quality management Quality assurance
Hazard Reliability
objectives, and to be rigorous in achieving those
objectives. All of this is simply good management.
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