3

Dual processes

in reasoning?*

P. C. WASON
University

College London

J. ST. 6. T. EVANS
Plymouth

Polytechnic

Abstract
Previous results have shown that the introductionof negatives into thesentences used in a deductive problem affected behavior in a systematic way
which was independant of the logical structure of the problem. In the present
investigation,
the subjects were asked to justify their responses whenreasoning about such sentences. In accordance with previous results, theresponses were dominated by the terms in the sentences regardless of whether
they were negated. However, the justifications did vary when negatives wereintroduced in accordance with the logical consequences of the responses. Theinterpretation of these justifications as causes of behavior seemed implausible.
It was suggested that they were rationalizations, or that there was at least
some form of dual processing between behavior and conscious thought.

The aim of this investigation
is to elucidate the character of the reasons given
for attempted
solutionsto the selection task, or four-card problem (Wason,
1966, 1968a). The problem is now fairly well known. In essence it consists inestablishing
the truth value of a conditional
sentence,e.g., ‘If a card has avowel on one side, then it has an even number on the other side’, by selecting
for inspection
the necessary
and sufficient
cards from a set consistingof avowel, a consonant,an even number and an odd number (under the restrictionthat each has a letter on one side and a number
on the other side). The
solutionis to select the vowel and the odd number because only these two* We thank I. Keddie for conducting
theexperiment,
and Dr. Neal Smalley for invaluable criticism. First author’s address:

Psycholinguistics
Research Unit, Woltson
House, 4, Stephenson Way, London N.W. 1
2HE.
Cognition

3(2). pp. 141 ~- 1.54

P. C. Wason and J. St. B. T Evansvalues on the same card could falsify the test sentence; the even number could
merely verify it vacuously.
But previous studies (with abstract material) havedemonstrated
that the most frequenterroneoussolutions
conSist in selecting
the values mentioned
in the test sentence.
The problem
is recalcitrant
tocorrection(Wason 1969a), and its difficulty
is not restricted to test sentenceswith the surface structureof a conditional;
in a recent version (Wason andGolding,1974) the sentence
is an assertion
e.g., ‘a letter is above eachnumber’.
The reader might well expect some justification
for yet another paper on
the problem.
The issues suggested by previous research still remain puzzlingand have only recently been investigatedsystematically.
For instance,
Bracewell (1974)
has argued that the subjects’remarks,
when confronted
bysubsequent
contradictions
to their initial choice, (e.g., ‘That is doing it theother way round’) are ‘correct’ inferences
based on inadequatepremises: The
subject is supposed to lack access to all the implicit features of the problem.
Our view is that such utterances
are rationalizations
determinedby erroneous
selections.
The issue is of some generality,
and the present study shifts theargument
to the character of elicited reasons which accompany
the choice ofcards. The problem has also been turned to other purposes, e.g., a critique offormal operations(Wason, 1975), the logic of natural language (Van Duyne,1974) and interhemisphericdifferencesin reasoning(Gelding,
Reich and
Wason, 1974). It has, in fact, become a tool for investigatinga variety oftheoreticalissues rather than an object of study in its own right.
An information-processing
model (Johnson-Laird
and Wason, 1970) has
been postulated
as an explanationof performance.
A subject’s
degree ofinsight into the problem
is defined
as a functionof his appreciation
thatfalsification of the test sentence
is more relevantto the solution
than its
verification. Goodwin
and Wason (1972)
found a correlation
betweenthe
postulateddegrees of insight (defined by choice of cards) and reasons given
for the choice.
Evans and Lynch (1973), however, adduced evidence that error is due not
to a tendency
to verify but to a tendency
to ‘match’ the mentioned
cards withthe actual cards. When the consequentof the.conditional
was negated, theyobserved a highly significant
tendency
for a subject to be correct for apparently spurious reasons. For example, given the sentence,‘if there is a W on one
side of a card, then there is not a 9 on the other side’, the W and the 9 tended
to be (correctly)
selected. A number
which is not 9 available, as (say) 8, is(correctly)
rejected.
This result might seem to indicatethat negating
theconsequent
allows the subjects to be ‘right’ because they simply ignore the‘not’. The phenomenon,
however, is more general. When the antecedentwasnegated, they observed a highly significant
tendency
for the value mentioned

ha1

processes

in reasoning?

143

to be (wrongly)
selected. Given the sentence,‘If there is not a T on one sideof a card, then there is a 5 on the other side’, the T and the 5 tended to be
selected although
the correct solution would be to select the letter other than
T and the number other than 5.
Evans (1972b)
argues that matchingbias is a hypothesis
based on a
statisticalregularity
and that it il,teracts with the logical processes demandedby the problem.
Its lack of theoreticalstatus has been challenged
by VanDuyne (1973). But whatever its interpretation,
the results obtained by Evansand Lynch (1973) cast some doubt on the Johnson-Laird
and Wason (1970)
model. Verificationand matchingcoincide (under affirmative
sentences),
butmatching
is evidently
more fundamental
because it appears indifferent
to thepresence of a negative. The thought processes elicited by this problem seem to
be more primitive
than had been supposed.
Evans and Lynch did not,however, ask their subjects to give reasons for their solutions.
The present
study aims to see how solutions are related to reasons when the consequentofthe conditional
is negated. On this particular rule matching bias should induce
the logicallycorrect solution,but obviously
for the wrong reasons. It is amatter of considerable
interest to see whether the subjects’ justifications
still
reflect the ‘complete
insight’ observed
by Goodwin
and Wason (1972) toaccompany
the correct solutions.

Experiment
Performance
under a test sentencewith an unnegatedconsequent
was compared with that under a negated consequent.
The sentences had the following
general form:(1)‘If there is a [specified letter] on one side of a card, then there will be a[specified number]on the other side.’(2)‘If there is a [specified letter] on one side of a card, then there will not
be a [specified number]on the other side.’
The four cards which accompany
each test sentence
have the following
general form: The specified letter (L+); the specified number(N+); an unspecified letter (L-); and an unspecified
number (N-).
Under (1) the solution
is (L+) and (N-); under (2) it is (L+) and (N+). It
was predictedthat values of (L+) and (N+) would be selected under both (1)and (2), the solutions
being nominallywrong under (1) and nominallyrightunder (2).
Reasons for either selecting or rejecting
each card were written down by
the subjects, but no predictions
were made about their content.
A related group design was used. Twenty-four
unpaid volunteer
students of144

P. C. Wason and J. St. B. T Evans

the City of London
Polytechnic,
who had no previous experience
with theproblem,
were assigned alternately
to one of two groups and tested individually. One group first performedthe ‘affirmativetask’ and then the ‘negativetask’. The other group performed
the tasks in the opposite order.
The subjects were first acquainted
with the fact that all the cards had aletter on one side and a number
on the other side by inspectionof an‘example set’ of eight cards which were not actually used in the experiment.
Each test sentence was presented with four cards displaying (respectively)
thetwo specified and two unspecified
symbols. For each subject all the symbols
were different
on the two tests, and the order of presenting
the cards fromleft to right was random. After the subjects had examinedthe ‘example sets’of cards, the following
instructions
were read by them, and they were thenFinally,
the salient points wereasked whether
they had any questions.
repeated by the experimenter
to clarify the procedure.
‘You will be given two sheets of paper one at a time. At the top of the
sheet is stateda simple rule connecting
the combinationsof letters andnumbers
which are written on the cards. The rule only applies to the cards infront of you and it may be true or false. You must decide which card (orcards) need definitely
to be turned over in order to establish whether the rule
is true or false.
‘Below the cards, on the left-handside of the sheet, the identification
numbersof the cards are arranged in columns. When you have decided whichcards must be turned over, place a “Yes” or “No” in the column next to theappropriate
identification
number:“Yes” - for turning the card over“No” - for leaving the card alone
I also want you to write down your reasons for choosing to examine or toignore each card in the third column.
The problem
is not so easy as it looks, so please think carefully
beforegiving your answer.’
No time limits were imposed,
and the subjects were not allowed to turnover any of the cards.

Quantitative

results

The frequency
of different
selections is presented
in Table 1. It will be notedthat there is such strong support for the predictionthat statistical evaluationis unnecessary.
Fifteen out of the 24 subjects were correct in the negative task
comparedwith none in the affirmativetask. Furthermore,exactly half thesubjects made the matching
response (L+) and (N+) in the affirmativetask,

Dual processes in reasoning?

145

out of a possible 15 responses.
It will also be noted that there is no apparent
order effect. However, there were 8 out of 24 atypical responses (‘others’)
definedas selections
which either omit (L+) or include (L-),
in the affirmative task, comparedwith three in the negative task (of these 11 cases, four
consisted in the selectionof all four cards). Previous research (Johnson-Laird
and Wason, 1970) suggests that atypical responses are probably
indicativeofeither misunderstandingor guessing. No reason is apparent
for the relatively
greater number of such responses in the affirmative
task.
Table

1.

Frequencyof responses in affirmative and negative tasks
Affirmative

Order of permormance/

Negative

1st

2nd

Total

1st

2nd

Total

values selcted(L+) (N+)

6

6

@+I
&+I W-1others

2
0
4

2
0
4

12
4
o*
8

9
2
0
1

6
4
0
2

15*
6
0
3

12

12

24

12

12

24

N

* = Correct response.

Qualitative

results

A small minorityof protocols
were so idiosyncraticthat no consistent
thought
process could be inferred from them. An attempt was first made toclassify
the remainder
with respect
to selectedcards into the following
categories:(a) Verification,(b) falsificationand (c) matching.
These exemplars illustrate the criteria for assigning a protocol to each category.
(a) Verification.
‘Should be J on the other side if rule holds.’ ‘If there is not
a 3 on the other side the rule is proved. ’ ‘To verify the rule as to there being aisB on the opposite
side. ’ ‘If there is an A on the other side the statement
true. ’(b) Falsification.
‘If there is a 6 on the other side, then the statement
isfalse.’ ‘To see if there is a Y on the other side to disprove the statement.’‘If
rule is true, then there will not be a 2. If rule is false there will be.’ ‘If thiscard is overturned
and there is an F the statement
is false.’(c) Matching.
‘Uppermost
symbols
may correspondwith those on theback.’ ‘It would be possible for there to be C on the other side.’ ‘If it has a 4

146

P. C. Wason and J. St. B. T. Evansoverleaf then Q and 4 are associated. ’ ‘The rule only says that 7 is related toJ.’Some difficulties
were experienced
in attempting
to distinguishbetweenverificationand matching.
For example,‘To find out if there is a 4 on theother side’ could be interpreted
as a weak statementof verification.
Similarly,‘To check the truth or falsity of the statement’seems like a simple compliancewith the instruction.
The source of the difficultyis that terms indicativeofverification
are linguisticallyunmarked.
This difficulty
does not arise with thefalsification
category because its terms are linguisticallymarked, e.g., ‘untrue’,‘disproof’or cognate
expressions.
Hence a more stringent
decisionwasadopted:Each protocol was classified as either ‘falsification’or ‘not falsification’.
In the affirmative
task four out of the 24 protocols
were classified as‘falsification’.
In the negative task 1 1 out of 24 were classified as falsification,nine of which were associatedwith correct solutions.
Of these nine, eightoccurred in the group who performed
the negative task first. This significant
order effect (p < 0.05, Fisher exact test) may have been due to the fact thatthe subjects were not allowed to turn over the cards. This may have induced
frustrationand hence diminishedinterest for the second task although
there
was no evidence for this supposition.
The remaining
two subjects,
who yieldedfalsification
protocols
but incorrect solutionsin the negative task, selected in each case just (L+), one in
the first performanceand the other in the second performance.
These cases
reveal only an ‘indirect falsification
effect’, i.e., a reason in terms of falsification
to justify
the selectionof the (unnegated)
antecedentwhen theconsequentis negated,e.g., ‘Easiest thing to do to prove the rule false is toturn T over to find out whether it is in fact also 5.’ This is distinguishedfromthea ‘direct falsification
effect’, i.e., a similar type of reason to justify
selection of the (negated) consequent.
Of the four subjects who yielded falsification
protocolsin the affirmativetask, three did so when that task was performed
second, and all four yieldedfasification
protocols in the negative task.
The protocolsof three subjects show how the reasons given for the choiceof the mentioned
cards are quite different in the affirmativeand negative
tasks when both make exactly the same matching
responses.
In order to ease
the readers’ comprehension,
the affirmativeand negative sentences have beencorrected
so that they are lexically equivalent.
It will be noted that all threecases reveal both a ‘direct’ and an ‘indirect’ falsification
effect. In addition,
the reasons given for not selecting the unmentioned
cards reveal a process of‘mismatch’.

Dual processes in reasoning?

Cards and responses

Negative

Affirmativetask

If there is a B .

task

there will not be a 3

If there is a B
there will be a 3.

Reasons

Reasons

then

147

then

G2.

S3

B

yes

‘If the rule was false, there
would be a 3 on the otherside. If true there would
not be a 3.
B and 3 should be takenof the sameas partassumption.’‘The rule only says that B
is related to 3. It does not
say anything
about there
being a logical sequenceof letters to numbers,
sono assumptions
about letters and numbers
otherthan B and 3 can be made.’3

yes‘If the rule was false, there
would be a B on the otherside.’‘As above.’

U

no‘The rule only states that
there
is
no
relation
between 3 and B. It does
not state whether
there
is a relation between othernumbers and letters.’‘Logicalargument

6

no‘As above.’‘As above.’

(32,

s2

B

yes

‘To see that

it is not a 3.’‘To ensure that the reverse
is 3.’

3yes‘To ensure
B.’that it is not a‘To ensure that the reverse
is B.’Uno‘It needthing.’

not

prove

any-

extension
above.’‘The
resultinconclusive.’

might

of

be

148

P. C. Wason and J. St. B. T. Evans

6

ll0

G2,

S6

B

yes

3

‘It needthing.’

not

prove

any-

‘The
resultinconclusive.’

might

be

‘If there is a 3 on the otherside, then the statement
is false.’‘If there is a 3 on theother side then the statement is true.’‘If there is a B on the otherside then the statement
is false.’‘If there is a B on the otherside, then the statement
istrue: otherwise it is false’.

U

n0‘Whatevernumberis on
the other side will notshow if statement
is trueor false.’‘Any number
may be on
the other side.’6

no‘Any letter may be on theother side, thereforenoway of knowing
if statement is true.’‘If numbers are fairly ranom, then there may be any
letter on the other side,
therebygiving no indication unless the letter is B.’

It will be noted that the protocols
differentiate
between the tasks, but at amore basic level they are similar. They reveal what might be called a ‘secondary matchingbias’: The subjects
not only select the values mentioned(‘matchingbias’), but justify their selections in terms of the named values on
the other side of the card.

Discussion
In the negative task (at least when it constitutes
the first test) the justifications for choice strongly
suggest logically appropriate
thought
processes. If
such reasons
had been associatedwith the unnegatedsentencesused inprevious
studies, they would have been interpreted
as indicating‘completeinsight’.
There are three hypotheses
which attempt
to reconcile
matching
responses with qualitative
observations
incompatible
with such matching:The
behaviorist hypothesis,
the rational hypothesis
and the dual process hypothe-Dual processes in reasoning?

149

sis. (These terms are intended
merely as mnemoniclabels which have only anapproximate
reference to the hypotheses
enumerated.)
The behaviorist
hypothesisis that the ‘reasons’ are verbal responses whichcannot be interpreted
as revealing anything
about the cause of behavior. Thishypothesis
is dubious
because reasons and tasks are correlated.
On the firsttask 8.3 percent (1 out of 12) of the affirmative
protocols
are classified as‘falsification’,comparedwith 75 percent (9 out of 12) of the negative protocols.
The rational hypothesisis that the reasons express the cause of the choices.
It follows that in the negative task the appropriate
reasons indicate a genuine
logical insight into the structure of the problem. But it is rather implausible
tosupposethat a genuine
insight would suddenly
vanish in the subsequentaffirmativetask. Furthermore,when the antecedent
rather than the consequent of the conditional
is negated (Evans and Lynch,1973), the subjects
tended to choose the negated value which, in this case, is logically inappropriate. If the effect of a negative is assumed to be the same on both theantecedentand consequentof a conditional
sentence,
it follows that thenegatedconsequentin the present study does not seem to confer genuine
insight into the logic of the conditional.
And it follows from this that therational hypothesis
is untenable.
It is, however, to be regretted that we did notinclude test sentences with a negated antecedentin the present study.
The dual process hypothesis
postulates
that performanceand introspection
reflect different underlying
processes. It makes two fundamental
assumptions:( 1) The processes
underlying
the reasoning
performance,e.g., matchingbias, are not generally available for introspective
report.
(2) Introspective
accounts
of performancereflecta tendency
for thesubject to construct a justification
for his own behavior consistent
with hisknowledgeof the situation.
The process specified in (2) might be termed ‘rationalization’although we
do not wish to emphasize
the motivational
aspects of the Freudianconcept.
More directly relevant is the work of social psychologists
who have shown aneed for individuals
to maintainconsistency
betweentheir beliefs (Zajonc,
1968).
There are several consequencesof the two assumptions.
It follows from
(1) that introspective
protocols
will be of little assistance in the construction
and validationof theories concernedwith predicting
behavior. It follows from
(1) and (2) that identificationof processes underlying
behavior will not bemuch help in predicting
the nature of associated introspective
protocols. The
latter will depend on what the subject perceives to be the requirementsof thesituation,in the light of which he will interpret his own behavior. Thus the
predominanceof verificationand falsification
among the explicitly
stated150

P. C. Wason and J. St. B. T. Evansprotocolsof the present experimentarises from the fact that the subject was
instructed
to test the truth value of an affirmativeand negative sentence(respectively).
He tends to interpret
his choice in terms appropriate
to thesecontexts.
It also follows from the two assumptions
that, instead of introspection revealing the causes of behavior, behavior is seen as one of the principal
causes of the introspection.
This reversal of the common
sense directionof
causality is reminiscentof the James-Langetheory of emotion.
But in what way does the presenceof a negativeelicit a justification
expressed predominantly
in terms of falsification?
One answer would be thata negative induces the idea of falsification
with respect to the terms which it
negates.
It does appear
that the matching
response
is susceptible
to aninteraction
betweena specified truth value and the syntacticalform of theconditional.
Evans (1972a)
instructedsubjects
to construct
verifying
andfalsifying
instancesof conditional
sentencesin which the components
weresystematicallynegated. On the first trial, under a verifying
instruction,
thematching
response was made to the negated antecedentin only two cases outof 48; but under a falsifying instruction,
it was made in 27 cases out of 48. Inother words, given a sentence in the form, ‘if not (L+) then (N+)‘, a verifying
instance
tendedto be constructed(correctly)as (L-)and (N+), but afalsifying instance constructed(incorrectly)as (L+) and (N+) rather than thecorrect(L-)
and (N-).
This accountilluminatesthe ‘direct falsification
effect’,but it leaves unexplainedthe ‘indirect
falsification
effect’ ~ theselectionof the unnegatedantecedentterms with appropriate
falsifying
reasons.
But perhaps
the explanation
is not so deep: Falsificationarisesbecause it fits both the responses and the context of the task.
In its strongest
form the dual process hypothesis,that response determines
conscious
thought, may be an oversimplification.
A weaker (but more plausible) assumption
is that there is a dialectical relation between them: A processof rapid continuous
feedback between tendencies
to respond and consciousness rather than two temporally
distinctphases. This ‘interpretive’
view ofreasoningin the selection
task has been well expressed by Smalley (1974):‘. . . reasoning is not the orderly, linear process we have sometimes imagined it
to be. The kind of reasoning
typified by orderly syllogistic
deductionfrompremises to conclusion[should be] replaced by a more disorderly
process inwhich extracted
features are organized into an interpretation. . . the process
is disorderlyin the sense that a shifting back and forth between various pieces
of information
may be necessary to come to an interpretation.’
The hypothesis
is formulated
in its strong form so that it can be tested. It is
well known that the processing of a negative normally imposes more cognitive
load than the processing of an affirmativeand consumes more time. Hence thedual process hypothesis
and the rational hypothesis
generate different predic-

Dual processes in reasoning?

1.51

tions. According
to the former, the cognitive load would be imposed primarily
in finding the ‘reasons’ (justifications);
accordingto the latter it would be
imposedprimarily
in determining
the response.
Hence the dual process
hypothesis
would predict that the ratio of ‘justification
time’ to ‘selection
time’ would be less for affirmative
than negative
sentences.
The rational
hypothesis
would predict the converse relation.
However, Smalley (personalcommunication)
has pointed out that the semantic representationof negatives
may be difficult
to express as sentences
regardless of which hypothesisiscorrect. He proposes the following simpler test. The rational hypothesis
would
predict that affirmatives
will be faster than negatives in both ‘selection time’and ‘justification
time’. If the prediction
is not confirmed,
then the alternative
dual process hypothesis
is corroborated.
This test can be made more economical and decisive by just considering‘selection time’.
Corroborative
evidence for the dual process hypothesis
is to be found inprevious results on the four-card problem (Wason and Johnson-Laird,1972).
These experimentssuggested that subjects tended to engage in highly distinctive rationalizations
to preserve an initial erroneous
solutionin the face ofcontradictoryevidence.
For example,
they may insist that the cards are‘irreversible’or acknowledge
that a card falsifies the rule but then deny its
relevance.
Such phenomena
seem to’reveal distinct thought processes which
fail to interact so that conflict may remain unresolved.
One experiment(Wason, 1969b) is particularly
vulnerable
to reinterpretation in terms of dual processing.
The solution
to the problem was presented,
and the task was to give reasons
why it was correct.
All the subjects
accomplishedthis, and the inference
was that they had been prevented from
imposing their own structureon the task. But an equally plausible interpretation is that the reasons did not reflect insight but were simply constructedto
fit the solution.
The rival interpretations
could be tested by presenting
erroneoussolutionsas ‘correct’. The dual process hypothesis
would predictthat ‘reasons’ would be found to satisfy the purported
correctnessof anycommonwrong solution.
It also follows that the verbal protocols(Goodwinand Wason, 1972) collected
to corroborate
the Johnson-Laird
and Wason(1970) model would not be interpreted
as independent
evidence for the stages
postulated
in the model. The protocols
reflect the choices which define thestages.
Circumstantial
evidence
for the hypothesis
may be found in an inductive
reasoningproblem (Wason, 1960, 1968b). The task was to discover a rule bygenerating
triads of numbers(with feedback about whether they conformed
to the rule). It was quite frequently
found that the same hypothesis
about therule would be reformulated
without awareness after the first formulation
hadbeen pronounced
wrong. For example, one subject announced
this rule on the152

P. C. Wason and J. St. B. T. Evansbasis of confirming
evidence:‘The rule is to start with a basic number,thendouble it and thirdly multiply
it by three.’ On being told it was wrong, five
more confirming
triads were generated,
and this rule was announced:‘The
rule is that the second number is double the first and two-thirdsof the third.’
The hypothesis,x 2x 3x, (where x = any whole number)continues
to exert
itself unconsciously
but allows a conscious displacement
to fulfill the requirements of the task.
The dual process hypothesis,
however, assumes that an individual’s
rationalizations may be wholly appropriate
when the problem
lies within his competenceor experience.
For example,
when the problem
is presented
in arealistic guise (e.g., Johnson-Laird,
Legrenzi and Sonino Legrenzi, 1972), it is
not at all difficult.
The familiar
content
obviates
the matching
response
becausethe structureof the problem
is readily apparent.
Indeed such a
response
seems to be elicitedby the perplexity
arousedby an abstract
conditional
because when a simpler logical connective(e.g., the disjunctive)issubstituted,
there is little evidence of matching(Wason and Johnson-Laird,
1969; Van Duyne, 1973).
The matching
response
may represent
in miniatureform a featureofintuitive
thought which is so characteristicof judgments
in unclear situations.
In this sense it may be analogous
to the ‘common-element
fallacy’ in disjunctive concept attainment(Bruner, Goodnow
and Austin,
1956, p. 168). In its
abstract
form the four-card
problemis almost certainly
not a satisfactory
techniquefor investigating
how the conditional
is construed
in a natural
language,but it may be a potential
techniquefor investigating
intuitive
andill-defined thought processes.
Such processes have been neglected by experimental
psychologists,
perhaps
because they are the antithesisof rational
thought.
And yet they are, ofcourse, a commonplacein scientificdiscovery. For example, mathematicians(e.g., PoincarC) sometimes
report that the solutions
to their problems
occur‘intuitively’
and that the conscious
constructionof the proof is worked out
after the insight. Indeed, since deduction
cannot generate new knowledge ana
inductionis philosophicallydiscredited,some kind of intuitive
process isprobablythe source of hypotheses.
We have argued that the results of thepresent experiment
representa (banal) example of such processes. The factthat a trivial alterationin the task predisposes
the subjects to be nominallyright or wrong is beside the point, and the use of conditional
sentence
structure to elicit the phenomena
is wholly fortuitous.

Dual processes

in reasoning?

153

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affectaitle comportement
de facon systematiqueindependantede la structure
logique du probleme. Dans l’enqubte pre-

154

P. C. Wason and J. St. B. T. Evanssente on demandait aux sujets de justifier
leurs reponses en raisonnant sur ces rbgles.
ConformCment
aux rksultats prkalables, lesrkponses Btaient dominkes par les termes
dans les rkgles sans se saucier de la nkgation.
Les justifications
variaientnkanmoinsquand on introduisait
des negatives conformes
aux conskquences
logiques
desrkponses. L’interpretationde ces justifications commecause du comportement
paraissait
peu plausible.
M est suggCrC
qu’elles Btaient des rationalisations
oti qu’ily avait au moins quelque forme de traitement
doubleentre
comportementetpens&e consciente.