Rationality and Reasoning

Jonathon St. B.T. Evans, David E. Over

• Publisher: Psychology Press
• Year: 2013
• eBook ISBN: 9781135472306
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

This book addresses an apparent paradox in the psychology of thinking. On the one hand, human beings are a highly successful species. On the other, intelligent adults are known to exhibit numerous errors and biases in laboratory studies of reasoning and decision making. There has been much debate among both philosophers and psychologists about the implications of such studies for human rationality. The authors argue that this debate is marked by a confusion between two distinct notions: (a) personal rationality (rationality1 Evans and Over argue that people have a high degree of rationality1 but only a limited capacity for rationality2. The book re-interprets the psychological literature on reasoning and decision making, showing that many normative errors, by abstract standards, reflect the operation of processes that would normally help to achieve ordinary goals. Topics discussed include relevance effects in reasoning and decision making, the influence of prior beliefs on thinking, and the argument that apparently non-logical reasoning can reflect efficient decision making. The authors also discuss the problem of deductive competence - whether people have it, and what mechanism can account for it. As the book progresses, increasing emphasis is given to the authors' dual process theory of thinking, in which a distinction between tacit and explicit cognitive systems is developed. It is argued that much of human capacity for rationality1 is invested in tacit cognitive processes, which reflect both innate mechanisms and biologically constrained learning. However, the authors go on to argue that human beings also possess an explicit thinking system, which underlies their unique - if limited - capacity to be rational.

Chapter One

Rationality in reasoning

Reasoning and decision making are topics of central importance in the study of human intelligence. Reasoning is the process by which we can apply our vast stores of knowledge to the problem at hand, deducing specific consequences from our general beliefs. Reasoning also takes place when we infer the general from the specific, by formulating and then testing new ideas and hypotheses. Rules for correct reasoning have been laid down by great thinkers in normative systems (principally logic and probability theory) and it is tempting to define, and evaluate, human rationality by referring only to these rules. However, we shall argue in this book that this approach is mistaken. The starting point for any understanding of human rationality should be behavioural: we must ask how decisions taken and actions performed serve the goals of the individual. Formulating and making use of logical and other rules has always had to rest on a more fundamental human ability to achieve behavioural goals.

The psychology of thinking has a long history, but the past 25 years or so have witnessed an explosion of research effort in the areas of decision making, judgement and reasoning, with many hundreds of experiments reported in the psychological literature. These studies are reviewed in detail in several recent textbooks (e.g. Baron, 1988; Evans, Newstead, & Byrne, 1993a; Garnham & Oakhill, 1994) and we will make no attempt to repeat the exercise here. In this book our purposes are theoretical and integrative: we seek to make sense of research in these vast literatures and to resolve some central theoretical issues of importance concerning rationality and the nature of human thinking. Hence our discussion of the published studies will be highly selective, although we believe focused on findings that are both important and representative of the area as a whole.

The aims of this book are three-fold. First, we address and attempt to resolve an apparent paradox of rationality that pervades in these fields. The issue of rationality is central to the first two chapters and underpins much of our later discussion. Next, we seek to achieve integration between the study of reasoning and decision making. Despite some recent efforts to bridge the gap, research in these two areas has proceeded largely in isolation. It seems to us that the mental processes of reasoning and decision making are essentially similar, although we shall see how an emphasis on rule-following as the basis of rationality has rendered this resemblance less than self-evident. Finally, we shall present a dual process theory of thinking which advances understanding of the phenomena we discuss and the psychological mechanisms underlying the kinds of rationality that people display in their reasoning and decision making.

The Rationality Paradox

The human species is far and away the most intelligent on earth. Human beings are unique in their cognitive faculties—for example, their possession of an enormously powerful linguistic system for representing and communicating information. They have learned not only to adapt to the environment but to adapt the environment to suit themselves; and they have organised vastly complex economic, industrial, and political systems. They have also developed a capacity for abstract thinking that has enabled them, among other things, to create logic and other normative systems for how they ought to reason.

What happens when representatives of this highly intelligent species are taken into the psychological laboratory to have their processes of thinking, reasoning, and decision making studied by psychologists? The surprising answer is that people seem to make mistakes of all kinds, as judged by the normative rules that human beings have themselves laid down. Many of these rule violations are systematic and arise in cases where a bias is said to exist. Some psychologists use this term as a necessarily pejorative one, but for us it will be descriptive, meaning only a departure from an apparently appropriate normative system. We are not talking here about minor aspects of human performance: systematic deviations from normative principles have been identified and reported in many hundreds of published studies within the past twenty years alone. Although we discuss the issues in general terms in this chapter, a number of specific examples of reasoning and decision biases will be discussed throughout this book. Lest this chapter be too abstract, however, we present a single example of the kind of thing we are talking about.

In syllogistic reasoning tasks, subjects are presented with two premises and a conclusion. They are instructed to say whether the conclusion follows logically from the premises. They are told that a valid conclusion is one that must be true if the premises are true and that nothing other than the premises is relevant to this judgement. Suppose they are given the following problem:

1.1	No addictive things inexpensive
	Some cigarettes are inexpensive
	Therefore, some addictive things are not cigarettes

On the basis of the information given, this syllogism is invalid. In other words, the conclusion does not necessarily follow from the premises. The class of cigarettes might include all addictive things, thus contradicting the conclusion. Of course, those cigarettes that were inexpensive would not be the ones that were addictive, but this is quite consistent with the premises. However, the majority of subjects given problems like 1.1 state erroneously that the conclusion does follow logically from the premises (71% in the study of Evans, Barston, & Pollard, 1983). Now suppose the problem is stated as follows:

1.2	No cigarettes are inexpensive
	Some addictive things are inexpensive
	Therefore, some cigarettes are not addictive things

The logical structure of 1.2 is the same as 1.1; all we have done is to interchange two of the terms. However, with problems of type 1.2 very few subjects say that the conclusion follows (only 10% in the study of Evans et al., 1983). What is the critical difference between the two? In the case of 1.1 the conclusion is believable and in the case of 1.2 it is not believable. This very powerful effect is known as “belief bias” and is discussed in detail in Chapter 5. It is clearly a bias, from the viewpoint of logic, because a feature of the task that is irrelevant given the instructions has a massive influence on judgements about two logically equivalent problems.

There seems to be a paradox. On the basis of their successful behaviour, human beings are evidently highly intelligent. The psychological study of deduction, on the other hand, appears to suggest that they are illogical. Although some authors in research on biases have been careful to qualify their claims about human behaviour, others have made fairly strong claims that their work shows people to be irrational (see Lopes, 1991, which discusses a number of examples). It is perhaps not surprising that research on biases in reasoning and judgement has come under close scrutiny from philosophers and psychologists who simply cannot accept these findings at face value and who take exception to the inferences of irrationality that are often drawn from the studies concerned. These criticisms mostly come from authors who take human rationality to be obvious, for the reasons outlined above, and who therefore conclude that there is something wrong with the research or its interpretation.

Evans (1993a) has discussed the nature of this criticism of bias research in some depth and classified the arguments into the following three broad groupings:

• the normative system problem;
• the interpretation problem; and
• the external validity problem.

The first major critique of bias research by a philosopher was that of Cohen (1981) whose paper includes examples of all three types of argument. The normative system problem, as Cohen discusses it, is that the subject may be reasoning by some system other than that applied in judgement by the experimenter. For example, psychologists studying deductive reasoning tend to assume a standard logic—such as extensional propositional logic—as their normative framework, whereas many other logics are discussed by logicians in the philosophical literature. Cohen (1982) suggested further that people might be using an old Baconian system of probability based on different principles from modem probability theory. We find this suggestion implausible—substituting, as it does, one normative system for another. However, the idea that rationality is personal and relative to the individual is important in our own framework as we shall see shortly.

A different slant on the normative system problem is the argument that conventional normative theories cannot be used to assess rationality because they impose impossible processing demands upon the subject. We would not, for example, describe someone as irrational because they were unable to read the text of a book placed beyond their limit of visual acuity, or because they could not recall one of several hundred customer addresses, or were unable to compute the square root of a large number in their heads. For this reason, Baron (1985) distinguishes normative theories from prescriptive theories. The latter, unlike the former, prescribe heuristics and strategies for reasoning that could be applied by people within their cognitive processing capabilities. For example, people cannot be expected to internalise probability theory as an axiomatic system and to derive its theorems, but they can learn in general to take account of the way in which the size and variability of samples affects their evidential value.

In the case of deductive reasoning, this type of argument has been proposed in several recent papers by Oaksford and Chater (e.g. 1993, 1995). They point out that problems with more than a trivial number of premises are computationally intractable by methods based on formal logic. For example, is is known that to establish the logical consistency of n statements in propositional logic requires a search that increases exponentially with n. Oaksford and Chater go on to argue that the major theories of deductive reasoning based on mental logic and mental models (discussed later) therefore face problems of computational intractability when applied to non-trivial problems of the sort encountered in real life, where many premises based on prior beliefs and knowledge are relevant to the reasoning we do. In this respect the argument of Oaksford and Chater bears also upon the external validity problem, also discussed later.

The interpretation problem refers to the interpretation of the problem by the subject, rather than the interpretation of the behaviour by the psychologist. The latter is a problem too, but one which belongs under the third heading, discussed below. The interpretation argument has featured prominently in some criticism of experimental research on deductive reasoning. For example, in a very influential paper, Henle (1962) asserted that people reason in accordance with formal logic, despite all the experimental evidence to the contrary. Her argument is that people’s conclusions follow logically from their personalised representation of the problem information. When the conclusion is wrong, it is because the subject is not reasoning from the information given: they may, for example, ignore a premise or redefine it to mean something else. They might also add premises, retrieved from memory. Henle illustrates her argument by selective discussion of verbal protocols associated with syllogistic reasoning. There are some cases, however, in which her subjects appear to evaluate the conclusion directly without any process of reasoning. These she classifies as instances of “failure to accept the logical task”.

Another version of the interpretation problem that has received less attention than it deserves is the argument of Smedslund of a “circular relation between logic and understanding” (see Smedslund, 1970, for the original argument and 1990 for a recent application of it). Smedslund argues that we can only decide if someone is reasoning logically if we presume that they have represented the premises as intended. Conversely, we can only judge their understanding of the problem information if we assume that they have reasoned logically Smedslund’s surprising conclusion from his discussion of this circularity is that “the only possible coherent strategy is always to presuppose logicality and regard understanding as a variable”. This argument was scrutinised in detail by Evans (1993a) who refuted it by discussion of the specific example of conditional inference. He showed that subjects’ reasoning in such cases is not logically consistent with any interpretation that can be placed upon the conditional sentence and nor is there logical consistency between reasoning on one problem and another.

Perhaps the most potentially damaging critique of bias research is that based on the external validity problem. In its least sympathetic form, as in Cohen’s (1981) paper, the argument can aim to undermine the value of the research fields concerned on the basis that they study artificial and unrepresentative laboratory problems. Consider, for example, the Wason selection task (Wason, 1966), which we discuss in some detail later in this book. Devised as a test of hypothesis testing and understanding of conditional logic, this problem is solved— according to its conventional normative analysis—by less than 10% of intelligent adult subjects, and has become the single most studied problem in the entire reasoning literature (see Evans et al., 1993a, Chapter 4, for a detailed review). Cohen attempted to dismiss the phenomenon as a “cognitive illusion”, analogous to the Muller-Lyer illusion of visual perception. If he is right, then many researchers have chosen to spend their time studying a problem that is wholly unrepresentative of normal thinking and reasoning and that presents an untypically illogical impression of human thought. We disagree with Cohen, but we will nevertheless consider in some detail how performance on this particular task should be interpreted. Where we will agree with him is in rejecting the notion that the selection task provides evidence of irrationality. However, unlike Cohen we believe that study of this task has provided much valuable evidence about the nature of human thought.

Other aggressive forms of the external validity argument include suggestions that bias accounts are proposed to accord with fashion and advance the careers of the psychologists concerned and that researchers create an unbalanced picture by citing disproportionately the results of studies that report poor reasoning (see Berkeley & Humphreys, 1982; Christensen-Szalanski & Beach, 1984). A milder version of the argument has been presented by such authors as Funder (1987) and Lopes (1991) who, like us, are sympathetic to the research fields but concerned by interpretations of general irrationality that are placed upon them. Experiments that are designed to induce errors in subjects’ performance are valuable in advancing our theoretical understanding of thought processes. It is a mistake, however, to draw general inferences of irrationality from these experimental errors. As an analogy, consider that much memory research involves overloading the system to the point where errors of recall will occur. This provides useful experimental data so that we can see, for example, that some kinds of material are easier to recall than others, with consequent implications for the underlying process. Such research is not, however, generally used to imply that people have bad and inadequate systems of memory. So why should explorations of cognitive constraints in reasoning be taken as evidence of poor intelligence and irrationality?

Our own theoretical arguments stem from an attempt to resolve the problems outlined in this section and to address some of the specific issues identified. In doing this we rely heavily upon our interpretation of a distinction between two forms of rationality, first presented by Evans (1993a) and by Evans, Over, and Manktelow (1993b).

Two ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Foreword
• Preface and acknowledgements
• 1. Rationality in reasoning
• 2. Personal goals, utility, and probability
• 3. Relevance, rationality, and tacit processing
• 4. Reasoning as decision making: The case of the selection task
• 5. Prior belief
• 6. Deductive competence
• 7. A dual process theory of thinking
• References
• Author index
• Subject index