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Dual process theories of reasoning

In discussing the belief bias effect earlier, I mentioned that there was evi-dence of a conflict between two types of thought processes, one reasoning Table 7.1 Examples of four kinds of syllogisms presented by Evans et al. (1983) together with the percentage rates of acceptance of each argument as valid over three experiments

Type Example Rate

Valid-Believable No police dogs are vicious 89%

Some highly trained dogs are vicious Therefore, some highly trained dogs are not police dogs

Valid-Unbelievable No nutritional things are expensive 56%

Some vitamin tablets are expensive Therefore, some vitamin tablets are not nutritional

Invalid-Believable No addictive things are inexpensive 71%

Some cigarettes are inexpensive

Therefore, some addictive things are not cigarettes

Invalid-Unbelievable No millionaires are hard workers 10%

Some rich people are hard workers

Therefore, some millionaires are not rich people

logically according to the instructions and the other prompting people to respond on the basis of their prior beliefs. Of particular interest are the problems that bring logic and belief into conflict: Valid-Unbelievable and Invalid-Believable. There is evidence that logical performance on these con-flict problems declines sharply with age, while performance on problems where belief and logic agree is unaffected (Gilinsky & Judd, 1994). This can be linked theoretically with findings reported in a large programme of study of individual differences in reasoning ability (Stanovich, 1999). Stanovich found that people with high general intelligence scores were much better able to deal with belief–logic conflict problems, effectively suppressing belief influences in order to find the logical solutions. The link is that the cognitive basis of general intelligence scores, in particular working memory capacity, declines with age.

Stanovich’s results generally support a dual processing account of think-ing and reasonthink-ing (see also Evans & Over, 1996). It seems that we think using two different cognitive systems. The first system introduces prior knowledge based on associative learning and causes us almost compulsively to contextualize any problem we may be given to consider. By this I mean that we relate every problem to prior knowledge that we have which appears relevant to it. Although helpful in many real life situations, this contextual-ization may result in belief biases when we are supposed to be reasoning abstractly or logically, only considering the information in front of us. The second system does allow abstract reasoning, but only seems to be well developed in people of very high general intelligence. Stanovich has also shown that performance on the abstract form of the Wason selection task is related to general intelligence, whereas performance on realistic versions is not. This makes sense because the first system can provide solutions to typical realistic versions by generalizing past experience, whereas the second system is needed for the abstract task where there is no helpful prior knowledge to be added to the context.

The rationality debate

Research on deductive reasoning was developed during a period in which psychologists were content to follow many philosophers in regarding logic as a model for rational thinking (Evans, 2002). If we hold fast to this view, after the past 40 years or so of intensive investigation of deductive reasoning, then we should feel very concerned indeed about human rationality. As this brief survey has indicated, people – typically university students – given reasoning problems in the laboratory, make many errors. They frequently give logically incorrect answers to abstract reasoning problems and show biases indicative of shallow processing, such as matching bias in conditional reasoning and mood and figural biases in syllogistic reasoning. Introducing realistic content does not induce better logical reasoning, as was once thought. People’s reasoning is highly influenced by content and context that are logically

irrelevant to the task set, and the knowledge and belief introduced is just as likely to bias as to debias responses from a logical point of view.

Faced with these findings, psychologists (and to a lesser extent philo-sophers) have felt it necessary to resolve what Evans and Over (1996) term the “paradox of rationality”. The human species is highly successful and has succeeded in adapting the environment to its own needs, inventing science, technology, and so on. We seem to be a very intelligent species. So why are representatives of the human race generally so poor at solving reasoning tasks set in the psychological laboratory? Discussions of rationality in rea-soning experiments have turned on three major issues. The first of these is the normative system problem. Perhaps people seem illogical because formal logic provides a poor framework for assessing the rationality of everyday reasoning. Psychologists have in fact been somewhat naïve in adopting standard textbook logic as a normative reference, and have lacked aware-ness that such systems have been rejected by contemporary philosophical logicians precisely because they cannot be mapped onto natural language and everyday reasoning (Evans, 2002).

As an example, many psychologists have treated the conditional state-ment “If p then q” as though it represented a relationship of material impli-cation between p and q. Such a representation means that the conditional is true unless we have a case of p and not-q and logically equivalent to the statement “Either not p or q”. Suppose I make this statement:

If I am in London, then I am in France.

If I am in Plymouth when I make this statement and if the conditional is material, then you would have to say the statement is true. A material con-ditional is equivalent to:

Either I am not in London or I am in France.

Since I am in Plymouth, and therefore not in London, the first part of the disjunction is confirmed so the statement is true. However, it is self-evident that the conditional statement is false. Many philosophers consequently reject the material conditional. What we actually do is to imagine the world in which I am in London and ask whether I would be in France. Evidently we would be in England, so the statement is false.

A second issue is known as the interpretation problem. Perhaps partici-pants construe the task differently than the experimenter intended. Then their conclusions may follow logically from their personalized interpretation of the problem. Consider the following inference:

If there is an A on the card, then there is a 3 on the card.

There is a 3 on the card.

Therefore, there is an A on the card.

Many psychologists would regard this as a fallacy and mark anyone endorsing it as committing an error. When presented with abstract materials like these, the evidence is that intelligent adults frequently do agree that this conclusion follows (Evans et al., 1993). The problem is that the inference does follow logically if people interpret the statement as meaning “If and only if there is an A on the card, then there is a 3 on the card”. Moreover, it is not unreasonable for them to make such an interpretation, as this bicondi-tional reading is often intended when we use condibicondi-tionals in everyday dis-course. When people are given realistic conditionals, then they will make the above “fallacy” when only p seems to lead to q as in:

If he is over 18 years of age, then he is entitled to vote.

but they will not make it when the statement is clearly one way, as in:

If he is 18 years of age, then he is an adult.

In fact, no-one would infer that an adult must be 18 years of age. So the

“error” would not occur in everyday reasoning and the abstract problem can be regarded as ambiguous in interpretation.

The third issue is the external validity problem. This is the argument that many of the reasoning problems used in the laboratory are artificial and unrepresentative of real-world reasoning. Hence, people may be more rational than the experiments suggest. On this view, problems such as the Wason selection task provide cognitive illusions that tell us interesting things about how people think, but are not to be taken as measures of rationality in reasoning. This is analogous to saying that the visual illusions studied by psychologists are informative about the visual system, even though that system provides highly accurate representations of the world most of the time.

The force of these three arguments, taken together, makes it difficult to argue that the biases observed in deductive reasoning experiments are neces-sarily indicative of irrationality in human beings. However, this was not the objective for most of the psychologists working in this field anyway. As with topics discussed in many other chapters of this book, the study of biases and cognitive illusions in deductive reasoning has proved very helpful in the development of our theoretical understanding of human thought processes.

SUMMARY

• The deductive reasoning paradigm investigates the ability of ordinary people to solve logical reasoning problems. Hence, systematic departures from logical solutions are normally regarded as biases.

• One such well-established effect is the matching bias, which is a tendency

to focus on the explicit content of sentences, such as conditionals, regardless of whether propositions contain a negation that reverses their logical significance.

• While logically irrelevant, the content and context used to frame deduct-ive reasoning problems have marked influence on the responses that participants give. Sometimes realistic material affects people’s ability to perceive the logical validity of arguments.

• Dual process theory accounts for some reasoning biases by positing competing systems of reasoning. Pragmatic processes associated with implicit systems of cognition may interfere with people’s ability to apply abstract general reasoning in compliance with the instructions.

• Logic is nowadays disputed as the appropriate normative system for evaluating reasoning, so there is a major debate about the implications that reasoning biases have for human rationality.

FURTHER READING

For a broad discussion of the deductive reasoning paradigm and the major psychological phenomena associated with it, the reader is referred to Evans (2002). More detailed discussion of some of the biases in this literature is provided by Manktelow (1999). Those readers who are particularly inter-ested in the implications of this work for the debate about human rationality should consult Evans and Over (1996) and Stanovich (1999).

REFERENCES

Evans, J. St. B. T. (1989). Bias in human reasoning: Causes and consequences. Hove, UK: Lawrence Erlbaum Associates Ltd.

Evans, J. St. B. T. (1998). Matching bias in conditional reasoning: Do we understand it after 25 years? Thinking and Reasoning, 4, 45–82.

Evans, J. St. B. T. (2002). Logic and human reasoning: An assessment of the deduc-tion paradigm. Psychological Bulletin, 128, 978–996.

Evans, J. St. B. T., Barston, J. L., & Pollard, P. (1983). On the conflict between logic and belief in syllogistic reasoning. Memory & Cognition, 11, 295–306.

Evans, J. St. B. T., Handley, S. J., Harper, C., & Johnson-Laird, P. N. (1999). Reason-ing about necessity and possibility: A test of the mental model theory of deduction.

Journal of Experimental Psychology: Learning, Memory, and Cognition, 25, 1495–1513.

Evans, J. St. B. T., & Lynch, J. S. (1973). Matching bias in the selection task. British Journal of Psychology, 64, 391–397.

Evans, J. St. B. T., Newstead, S. E., & Byrne, R. M. J. (1993). Human reasoning: The psychology of deduction. Hove, UK: Lawrence Erlbaum Associates Ltd.

Evans, J. St. B. T., & Over, D. E. (1996). Rationality and reasoning. Hove, UK:

Psychology Press.

Gigerenzer, G., & Hug, K. (1992). Domain-specific reasoning: Social contracts, cheating and perspective change. Cognition, 43, 127–171.

Gilinsky, A. S., & Judd, B. B. (1994). Working memory and bias in reasoning across the life-span. Psychology and Aging, 9, 356–371.

Griggs, R. A., & Cox, J. R. (1982). The elusive thematic materials effect in the Wason selection task. British Journal of Psychology, 73, 407–420.

Handley, S. J., & Evans, J. St. B. T. (2000). Supposition and representation in human reasoning. Thinking and Reasoning, 6, 273–312.

Johnson-Laird, P. N., & Byrne, R. (1991). Deduction. Hove, UK: Lawrence Erlbaum Associates Ltd.

Klayman, J. (1995). Varieties of confirmation bias. The Psychology of Learning and Motivation, 32, 385–417.

Klayman, J., & Ha, Y. W. (1987). Confirmation, disconfirmation and information in hypothesis testing. Psychological Review, 94, 211–228.

Manktelow, K. I. (1999). Reasoning and thinking. Hove, UK: Psychology Press.

Manktelow, K. I., & Over, D. E. (1991). Social roles and utilities in reasoning with deontic conditionals. Cognition, 39, 85–105.

Oaksford, M., & Chater, N. (1998). Rationality in an uncertain world. Hove, UK:

Psychology Press.

Stanovich, K. E. (1999). Who is rational? Studies of individual differences in reason-ing. Mahway, NJ: Lawrence Erlbaum Associates Inc.

Wason, P. C., & Johnson-Laird, P. N. (1972). Psychology of reasoning: Structure and content. London: Batsford.

Part II