Thought

Alternative Title: thinking, thought process

Table of Contents

Introduction

Developments in the study of thought

Types of thinking

Thought, covert symbolic responses to stimuli that are either intrinsic (arising from within) or extrinsic (arising from the environment). Thought, or thinking, is considered to mediate between inner activity and external stimuli.

In everyday language, the word thinking covers several distinct psychological activities. It is sometimes a synonym for �tending to believe,� especially with less than full confidence (�I think that it will rain, but I am not sure�). At other times it denotes the degree of attentiveness (�I did it without thinking�) or whatever is in consciousness, especially if it refers to something outside the immediate environment (�It made me think of my grandmother�). Psychologists have concentrated on thinking as an intellectual exertion aimed at finding an answer to a question or the solution of a practical problem.

The psychology of thought processes concerns itself with activities similar to those usually attributed to the inventor, the mathematician, or the chess player, but psychologists have not settled on any single definition or characterization of thinking. For some it is a matter of modifying �cognitive structures� (i.e., perceptual representations of the world or parts of the world), while others regard it as internal problem-solving behaviour.

Yet another provisional conception of thinking applies the term to any sequence of covert symbolic responses (i.e., occurrences within the human organism that can serve to represent absent events). If such a sequence is aimed at the solution of a specific problem and fulfills the criteria for reasoning, it is called directed thinking. Reasoning is a process of piecing together the results of two or more distinct previous learning experiences to produce a new pattern of behaviour. Directed thinking contrasts with other symbolic sequences that have different functions, such as the simple recall (mnemonic thinking) of a chain of past events.

Historically, thinking was associated with conscious experiences, but, as the scientific study of behaviour (e.g., behaviourism) developed within psychology, the limitations of introspection as a source of data became apparent; thought processes have since been treated as intervening variables or constructs with properties that must be inferred from relations between two sets of observable events. These events are inputs (stimuli, present and past) and outputs (responses, including bodily movements and speech). For many psychologists such intervening variables serve as aids in making sense of the immensely complicated network of associations between stimulus conditions and responses, the analysis of which otherwise would be prohibitively cumbersome. Others are concerned, rather, with identifying cognitive (or mental) structures that consciously or unconsciously guide a human being�s observable behaviour. Developments in the study of thought Elements of thought

The prominent use of words in thinking (�silent speech�) encouraged the belief, especially among behaviourist and neobehaviourist psychologists, that to think is to string together linguistic elements subvocally. Early experiments revealed that thinking is commonly accompanied by electrical activity in the muscles of the thinker�s organs of articulation (e.g., in the throat). Through later work with electromyographic equipment, it became apparent that the muscular phenomena are not the actual vehicles of thinking; they merely facilitate the appropriate activities in the brain when an intellectual task is particularly exacting. The identification of thinking with speech was assailed by the Russian psychologist Lev Semyonovich Vygotsky and by the Swiss developmental psychologist Jean Piaget, both of whom observed the origins of human reasoning in children�s general ability to assemble nonverbal acts into effective and flexible combinations. These theorists insisted that thinking and speaking arise independently, although they acknowledged the profound interdependence of these functions.

Following different approaches, three scholars�the 19th-century Russian physiologist Ivan Mikhailovich Sechenov; the American founder of behaviourism, John B. Watson; and Piaget�independently arrived at the conclusion that the activities that serve as elements of thinking are internalized or �fractional� versions of motor responses. In other words, the elements are considered to be attenuated or curtailed variants of neuromuscular processes that, if they were not subjected to partial inhibition, would give rise to visible bodily movements.

Sensitive instruments can indeed detect faint activity in various parts of the body other than the organs of speech�e.g., in a person�s limbs when movement is thought of or imagined without actually taking place. Recent studies show the existence of a gastric �brain,� a set of neural networks in the stomach. Such findings have prompted theories to the effect that people think with the whole body and not only with the brain, or that, in the words of the American psychologist B.F. Skinner, �thought is simply behaviour�verbal or nonverbal, covert or overt.�

B.F. Skinner, 1971.AP/REX/Shutterstock.com

The logical outcome of these and similar statements was the peripheralist view. Evident in the work of Watson and the American psychologist Clark L. Hull, it held that thinking depends on events in the musculature: these events, known as proprioceptive impulses (i.e., impulses arising in response to physical position, posture, equilibrium, or internal condition), influence subsequent events in the central nervous system, which ultimately interact with external stimuli in guiding further action. There is, however, evidence that thinking is not prevented by administering drugs that suppress all muscular activity. Furthermore, it has been pointed out by researchers such as the American psychologist Karl S. Lashley that thinking, like other more-or-less skilled activities, often proceeds so quickly that there is not enough time for impulses to be transmitted from the central nervous system to a peripheral organ and back again between consecutive steps. So the centralist view�that thinking consists of events confined to the brain (though often accompanied by widespread activity in the rest of the body)�gained ground later in the 20th century. Nevertheless, each of these neural events can be regarded both as a response (to an external stimulus or to an earlier neurally mediated thought or combination of thoughts) and as a stimulus (evoking a subsequent thought or a motor response).

The elements of thinking are classifiable as �symbols� in accordance with the conception of the sign process (�semiotics�) that grew out of the work of philosophers (e.g., Charles Sanders Peirce), linguists (e.g., C.K. Ogden and Ivor A. Richards), and psychologists specializing in learning (e.g., Hull, Neal E. Miller, O. Hobart Mowrer, and Charles E. Osgood). The gist of this conception is that a stimulus event x can be regarded as a sign representing (or �standing for�) another event y if x evokes some, but not all, of the behaviour (both external and internal) that would have been evoked by y if it had been present. When a stimulus that qualifies as a sign results from the behaviour of an organism for which it acts as a sign, it is called a �symbol.� The �stimulus-producing responses� that are said to make up thought processes (as when one thinks of something to eat) are prime examples.

This treatment, favoured by psychologists of the stimulus-response (S-R) or neo-associationist current, contrasts with that of the various cognitivist or neorationalist theories. Rather than regarding the components of thinking as derivatives of verbal or nonverbal motor acts (and thus subject to laws of learning and performance that apply to learned behaviour in general), cognitivists see the components of thinking as unique central processes, governed by principles that are peculiar to them. These theorists attach overriding importance to the so-called structures in which �cognitive� elements are organized, and they tend to see inferences, applications of rules, representations of external reality, and other ingredients of thinking at work in even the simplest forms of learned behaviour.

The school of Gestalt psychology holds the constituents of thinking to be of essentially the same nature as the perceptual patterns that the nervous system constructs out of sensory excitations. After the mid-20th century, analogies with computer operations acquired great currency; in consequence, thinking came to be described in terms of storage, retrieval, and transmission of items of information. The information in question was held to be freely translatable from one �coding� to another without impairing its functions. What came to matter most was how events were combined and what other combinations might have occurred instead. The process of thought

According to the classical empiricist-associationist view, the succession of ideas or images in a train of thought is determined by the laws of association. Although additional associative laws were proposed from time to time, two invariably were recognized. The law of association by contiguity states that the sensation or idea of a particular object tends to evoke the idea of something that has often been encountered together with it. The law of association by similarity states that the sensation or idea of a particular object tends to evoke the idea of something that is similar to it. The early behaviourists, beginning with Watson, espoused essentially the same formulation but with some important modifications. For them the elements of the process were conceived not as conscious ideas but as fractional or incipient motor responses, each producing its proprioceptive stimulus. Association by contiguity and similarity were identified by these behaviourists with the Pavlovian principles of conditioning and generalization.

The W�rzburg school, under the leadership of the German psychologist and philosopher Oswald K�lpe, saw the prototype of directed thinking in the �constrained-association� experiment, in which the subject has to supply a word bearing a specified relation to a stimulus word (e.g., an opposite to an adjective, or the capital of a country). Introspective research led the members of the W�rzburg school to conclude that the emergence of the required element depends jointly on the immediately preceding element and on some kind of �determining tendency� such as Aufgabe (�awareness of task�) or �representation of the goal.� The last two factors were held to impart a direction to the thought process and to restrict its content to relevant material. Their role was analogous to that of motivational factors��drive stimuli,� �fractional anticipatory goal responses��in the later neobehaviouristic accounts of reasoning (and of behaviour in general) produced by Hull and his followers.

Hull�s theory resembled the earlier �constellation theory� of constrained association developed by Georg Elias M�ller. Hull held that one particular response will occur and overcome its competitors because it is associated both with the cue stimulus (which may be the immediately preceding thought process or an external event) and with the motivational condition (task, drive stimulus) and is thus evoked with more strength than are elements associated only with the cue stimulus or the motivational condition. The German psychologist Otto Selz countered that in many situations this kind of theory would imply the occurrence of errors as often as correct answers to questions and thus was untenable. Selz contended that response selection depends rather on a process of �complex completion� that is set in motion by an �anticipatory schema,� which includes a representation of both the cue stimulus and the relation that the element to be supplied must bear to the cue stimulus. The correct answer is associated with the schema as a whole and not with its components separately. Selz�s complex completion resembles the �eduction of correlates� that the British psychologist Charles E. Spearman saw as a primary constituent of intellectual functioning, its complement being �eduction of relations��that is, recognition of a relation when two elements are presented.

The determination of each thought element by the whole configuration of factors in the situation and by the network of relations linking them was stressed still more strongly by the Gestalt psychologists in the 1920s and �30s. On the basis of experiments by Wolfgang K�hler (on �insightful� problem solving by chimpanzees) and Max Wertheimer and his student Karl Duncker (on human thinking), they pointed out that the solution to a problem commonly requires an unprecedented response or pattern of responses that hardly could be attributed to simple associative reproduction of past behaviour or experiences. For them, the essence of thinking lay in sudden perceptual restructuring or reorganization, akin to the abrupt changes in appearance of an ambiguous visual figure.

The Gestalt theory has had a deep and far-reaching impact, especially in drawing attention to the ability of the thinker to discover creative, innovative ways of coping with situations that differ from any that have been encountered before. This theory, however, has been criticized for underestimating the contribution of prior learning and for not going beyond rudimentary attempts to classify and analyze the structures that it deems so important. Later discussions of the systems in which items of information and intellectual operations are organized have made fuller use of the resources of logic and mathematics. Merely to name them, they include the �psychologic� of Piaget, the computer simulation of human thinking by the American computer scientists Herbert A. Simon and Allen Newell, and extensions of Hull�s notion of the �habit-family hierarchy� by Irving Maltzman and Daniel E. Berlyne.

Also important is a growing recognition that the essential components of the thought process, the events that keep it moving in fruitful directions, are not words, images, or other symbols representing stimulus situations; rather, they are the operations that cause each of these representations to be succeeded by the next, in conformity with restrictions imposed by the problem or aim of the moment. In other words, directed thinking can reach a solution only by going through a properly ordered succession of �legitimate steps.� These steps might be representations of realizable physicochemical changes, modifications of logical or mathematical formulas that are permitted by rules of inference, or legal moves in a game of chess. This conception of the train of thinking as a sequence of rigorously controlled transformations is buttressed by the theoretical arguments of Sechenov and of Piaget, the results of the W�rzburg experiments, and the lessons of computer simulation.

Early in the 20th century, the French physician �douard Clapar�de and the American philosopher John Dewey both suggested that directed thinking proceeds by �implicit trial-and-error.� That is to say, it resembles the process whereby laboratory animals, confronted with a novel problem situation, try out one response after another until they sooner or later hit upon a response that leads to success. In thinking, however, the trials were said to take the form of internal responses (imagined or conceptualized courses of action, directions of symbolic search); once attained, a train of thinking that constitutes a solution frequently can be recognized as such without the necessity of implementation through action and sampling of external consequences. This kind of theory, popular among behaviourists and neobehaviourists, was stoutly opposed by the Gestalt school, whose insight theory emphasized the discovery of a solution as a whole and in a flash.

John DeweyEncyclop�dia Britannica, Inc.

The divergence between these theories appears, however, to represent a false dichotomy. The protocols of K�hler�s chimpanzee experiments and of the rather similar experiments performed later under Pavlov�s auspices show that insight typically is preceded by a period of groping and of misguided attempts at a solution that are eventually abandoned. On the other hand, even the trial-and-error behaviour of an animal in a simple selective-learning situation does not consist of a completely blind and random sampling of the behaviour of which the learner is capable. Rather, it consists of responses that very well might have succeeded if the circumstances had been slightly different.

Newell, Simon, and the American computer scientist J. Clifford Shaw pointed out the indispensability in creative human thinking, as in its computer simulations, of what they called �heuristics.� A large number of possibilities may have to be examined, but the search is organized heuristically in such a way that the directions most likely to lead to success are explored first. Means of ensuring that a solution will occur within a reasonable time, certainly much faster than by random hunting, include adoption of successive subgoals and working backward from the final goal (the formula to be proved, the state of affairs to be brought about). Motivational aspects of thinking

The problem to be taken up and the point at which the search for a solution will begin are customarily prescribed by the investigator for a subject participating in an experiment on thinking (or by the programmer for a computer). Thus, prevailing techniques of inquiry in the psychology of thinking have invited neglect of the motivational aspects of thinking. Investigation has barely begun on the conditions that determine when the person will begin to think in preference to some other activity, what he will think about, what direction his thinking will take, and when he will regard his search for a solution as successfully terminated (or abandon it as not worth pursuing further). Although much thinking is aimed at practical ends, special motivational problems are raised by �disinterested� thinking, in which the discovery of an answer to a question is a source of satisfaction in itself.

In the views of the Gestalt school and of the British psychologist Frederic C. Bartlett, the initiation and direction of thinking are governed by recognition of a �disequilibrium� or �gap� in an intellectual structure. Similarly, Piaget�s notion of �equilibration� as a process impelling advance from less-equilibrated structures, fraught with uncertainty and inconsistency, toward better-equilibrated structures that overcome these imperfections was introduced to explain the child�s progressive intellectual development in general. Piaget�s approach may also be applicable to specific episodes of thinking. For computer specialists, the detection of a mismatch between the formula that the program so far has produced and some formula or set of requirements that define a solution is what impels continuation of the search and determines the direction it will follow.

Neobehaviourism (like psychoanalysis) has made much of secondary reward value and stimulus generalization�i.e., the tendency of a stimulus pattern to become a source of satisfaction if it resembles or has frequently accompanied some form of biological gratification. The insufficiency of this kind of explanation becomes apparent, however, when the importance of novelty, surprise, complexity, incongruity, ambiguity, and uncertainty is considered. Inconsistency between beliefs, between items of incoming sensory information, or between one�s belief and an item of sensory information evidently can be a source of discomfort impelling a search for resolution through reorganization of belief systems or through selective acquisition of new information.

The motivational effects of such factors began receiving more attention in the middle of the 20th century, mainly because of the pervasive role they were found to perform in exploratory behaviour, play, and aesthetics. Their larger role in all forms of thinking has come to be appreciated and has been studied in relation to curiosity, conflict, and uncertainty. D.E. Berlyne Types of thinking

Philosophers and psychologists alike have long realized that thinking is not of a �single piece.� There are many different kinds of thinking, and there are various means of categorizing them into a �taxonomy� of thinking skills, but there is no single universally accepted taxonomy. One common approach divides the types of thinking into problem solving and reasoning, but other kinds of thinking, such as judgment and decision making, have been suggested as well. Problem solving

Problem solving is a systematic search through a range of possible actions in order to reach a predefined goal. It involves two main types of thinking: divergent, in which one tries to generate a diverse assortment of possible alternative solutions to a problem, and convergent, in which one tries to narrow down multiple possibilities to find a single, best answer to a problem. Multiple-choice tests, for example, tend to involve convergent thinking, whereas essay tests typically engage divergent thinking. The problem-solving cycle in thinking

Many researchers regard the thinking that is done in problem solving as cyclical, in the sense that the output of one set of processes�the solution to a problem�often serves as the input of another�a new problem to be solved. The American psychologist Robert J. Sternberg identified seven steps in problem solving, each of which may be illustrated in the simple example of choosing a restaurant:

Problem identification. In this step, the individual recognizes the existence of a problem to be solved: he recognizes that he is hungry, that it is dinnertime, and hence that he will need to take some sort of action.

Problem definition. In this step, the individual determines the nature of the problem that confronts him. He may define the problem as that of preparing food, of finding a friend to prepare food, of ordering food to be delivered, or of choosing a restaurant.

Resource allocation. Having defined the problem as that of choosing a restaurant, the individual determines the kind and extent of resources to devote to the choice. He may consider how much time to spend in choosing a restaurant, whether to seek suggestions from friends, and whether to consult a restaurant guide.

Problem representation. In this step, the individual mentally organizes the information needed to solve the problem. He may decide that he wants a restaurant that meets certain criteria, such as close proximity, reasonable price, a certain cuisine, and good service.

Strategy construction. Having decided what criteria to use, the individual must now decide how to combine or prioritize them. If his funds are limited, he might decide that reasonable price is a more important criterion than close proximity, a certain cuisine, or good service.

Monitoring. In this step, the individual assesses whether the problem solving is proceeding according to his intentions. If the possible solutions produced by his criteria do not appeal to him, he may decide that the criteria or their relative importance needs to be changed.

Evaluation. In this step, the individual evaluates whether the problem solving was successful. Having chosen a restaurant, he may decide after eating whether the meal was acceptable.

This example also illustrates how problem solving can be cyclical rather than linear. For example, once one has chosen a restaurant, one must determine how to get there, how much to tip, and so on. Structures of problems

Psychologists often distinguish between �well-structured� and �ill-structured� problems. Well-structured problems (also called well-defined problems) have clear solution paths: the problem solver is usually able to specify, with relative ease, all the steps that must be taken to reach a solution. The difficulty in such cases, if any, has to do with executing the steps. Most mathematics problems, for example, are well-structured, in the sense that determining what needs to be done is easy, though carrying out the computations needed to reach the solution may be difficult. The problem represented by the question, �What is the shortest driving route from New York City to Boston?� is also well-structured, because anyone seeking a solution can consult a map to answer the question with reasonable accuracy.

Ill-structured problems (also called ill-defined problems) do not have clear solution paths, and in such cases the problem solver usually cannot specify the steps needed to reach a solution. An example of an ill-structured problem is, �How can a lasting peace be achieved between country A and country B?� It is hard to know precisely (or, perhaps, even imprecisely) what steps one would take to solve this problem. Another example is the problem of writing a best-selling novel. No single formula seems to work for everyone. Indeed, if there were such a formula, and if it became widely known, it probably would cease to work (because the efficacy of the formula would be destroyed by its widespread use).

The solution of ill-structured problems often requires insight, which is a distinctive and seemingly sudden understanding of a problem or strategy that contributes toward a solution. Often an insight involves conceptualizing a problem or a strategy in a totally new way. Although insights sometimes seem to arise suddenly, they are usually the necessary result of much prior thought and hard work. Sometimes, when one is attempting to gain an insight but is unsuccessful, the most effective approach is that of �incubation��laying the problem aside for a while and processing it unconsciously. Psychologists have found that unconscious incubation often facilitates solutions to problems. Algorithms and heuristics

Other means of solving problems incorporate procedures associated with mathematics, such as algorithms and heuristics, for both well- and ill-structured problems. Research in problem solving commonly distinguishes between algorithms and heuristics, because each approach solves problems in different ways and with different assurances of success.

A problem-solving algorithm is a procedure that is guaranteed to produce a solution if it is followed strictly. In a well-known example, the �British Museum technique,� a person wishes to find an object on display among the vast collections of the British Museum but does not know where the object is located. By pursuing a sequential examination of every object displayed in every room of the museum, the person will eventually find the object, but the approach is likely to consume a considerable amount of time. Thus, the algorithmic approach, though certain to succeed, is often slow.

A problem-solving heuristic is an informal, intuitive, speculative procedure that leads to a solution in some cases but not in others. The fact that the outcome of applying a heuristic is unpredictable means that the strategy can be either more or less effective than using an algorithm. Thus, if one had an idea of where to look for the sought-after object in the British Museum, a great deal of time could be saved by searching heuristically rather than algorithmically. But if one happened to be wrong about the location of the object, one would have to try another heuristic or resort to an algorithm.

Although there are several problem-solving heuristics, a small number tend to be used frequently. They are known as means-ends analysis, working forward, working backward, and generate-and-test.

In means-ends analysis, the problem solver begins by envisioning the end, or ultimate goal, and then determines the best strategy for attaining the goal in his current situation. If, for example, one wished to drive from New York to Boston in the minimum time possible, then, at any given point during the drive, one would choose the route that minimized the time it would take to cover the remaining distance, given traffic conditions, weather conditions, and so on.

In the working-forward approach, as the name implies, the problem solver tries to solve the problem from beginning to end. A trip from New York City to Boston might be planned simply by consulting a map and establishing the shortest route that originates in New York City and ends in Boston. In the working-backward approach, the problem solver starts at the end and works toward the beginning. For example, suppose one is planning a trip from New York City to Paris. One wishes to arrive at one�s Parisian hotel. To arrive, one needs to take a taxi from Orly Airport. To arrive at the airport, one needs to fly on an airplane; and so on, back to one�s point of origin.

Often the least systematic of the problem-solving heuristics, the generate-and-test method involves generating alternative courses of action, often in a random fashion, and then determining for each course whether it will solve the problem. In plotting the route from New York City to Boston, one might generate a possible route and see whether it can get one expeditiously from New York to Boston; if so, one sticks with that route. If not, one generates another route and evaluates it. Eventually, one chooses the route that seems to work best, or at least a route that works. As this example suggests, it is possible to distinguish between an optimizing strategy, which gives one the best path to a solution, and a satisficing strategy, which is the first acceptable solution one generates. The advantage of optimizing is that it yields the best possible strategy; the advantage of satisficing is that it reduces the amount of time and energy involved in planning. Obstacles to effective thinking

A better understanding of the processes of thought and problem solving can be gained by identifying factors that tend to prevent effective thinking. Some of the more common obstacles, or blocks, are mental set, functional fixedness, stereotypes, and negative transfer.

A mental set, or �entrenchment,� is a frame of mind involving a model that represents a problem, a problem context, or a procedure for problem solving. When problem solvers have an entrenched mental set, they fixate on a strategy that normally works well but does not provide an effective solution to the particular problem at hand. A person can become so used to doing things in a certain way that, when the approach stops working, it is difficult for him to switch to a more effective way of doing things.

Functional fixedness is the inability to realize that something known to have a particular use may also be used to perform other functions. When one is faced with a new problem, functional fixedness blocks one�s ability to use old tools in novel ways. Overcoming functional fixedness first allowed people to use reshaped coat hangers to get into locked cars, and it is what first allowed thieves to pick simple spring door locks with credit cards.

Another block involves stereotypes. The most common kinds of stereotypes are rationally unsupported generalizations about the putative characteristics of all, or nearly all, members of a given social group. Most people learn many stereotypes during childhood. Once they become accustomed to stereotypical thinking, they may not be able to see individuals or situations for what they are.

Negative transfer occurs when the process of solving an earlier problem makes later problems harder to solve. It is contrasted with positive transfer, which occurs when solving an earlier problem makes it easier to solve a later problem. Learning a foreign language, for example, can either hinder or help the subsequent learning of another language. Expert thinking and novice thinking

Research by the American psychologists Herbert A. Simon, Robert Glaser, and Micheline Chi, among others, has shown that experts and novices think and solve problems in somewhat different ways. These differences explain why experts are more effective than novices in a variety of problem-solving endeavours.

Herbert A. Simon, 1978.Keystone/ZUMA Press/age fotostock

As compared with novices, experts tend to have larger and richer schemata (organized representations of things or events that guide a person�s thoughts and actions), and they possess far greater knowledge in specific domains. The schemata of experts are also highly interconnected, meaning that retrieving one piece of information easily leads to the retrieval of another piece. Experts devote proportionately more time to determining how to represent a problem, but they spend proportionately less time in executing solutions. In other words, experts tend to allocate more of their time to the early or preparatory stages of problem solving, whereas novices tend to spend relatively more of their time in the later stages. The thought processes of experts also reveal more complex and sophisticated representations of problems. In terms of heuristics, experts are more likely to use a working-forward strategy, whereas novices are more likely to use a working-backward strategy. In addition, experts tend to monitor their problem solving more carefully than do novices, and they are also more successful in reaching appropriate solutions. Reasoning

Reasoning consists of the derivation of inferences or conclusions from a set of premises by means of the application of logical rules or laws. Psychologists as well as philosophers typically distinguish between two main kinds of reasoning: deduction and induction. Deduction

Deductive reasoning, or deduction, involves analyzing valid forms of argument and drawing out the conclusions implicit in their premises. There are several different forms of deductive reasoning, as used in different forms of reasoning problems.

In conditional reasoning the reasoner must draw a conclusion based on a conditional, or �if�then,� proposition. For example, from the conditional proposition �if today is Monday, then I will attend cooking class today� and the categorical (declarative) proposition �today is Monday,� one can infer the conclusion, �I will attend cooking class today.� In fact, two kinds of valid inference can be drawn from a conditional proposition. In the form of argument known as modus ponens, the categorical proposition affirms the antecedent of the conditional, and the conclusion affirms the consequent, as in the example just given. In the form known as modus tollens, the categorical proposition denies the consequent of the conditional, and the conclusion denies the antecedent. Thus:

If today is Monday, then I will attend cooking class today. I will not attend cooking class today. Therefore, today is not Monday.

Two other kinds of inference that are sometimes drawn from conditional propositions are not logically justified. In one such fallacy, �affirming the consequent,� the categorical proposition affirms the consequent of the conditional, and the conclusion affirms the antecedent, as in the example:

If John is a bachelor, then he is male. John is male. Therefore, John is a bachelor.

In another invalid inference form, �denying the antecedent,� the categorical proposition denies the antecedent of the conditional, and the conclusion denies the conclusion of the conditional:

If Othello is a bachelor, then he is male. Othello is not a bachelor. Therefore, Othello is not male.

The invalidity of these inference forms is indicated by the fact that in each case it is possible for the premises of the inference to be true while the conclusion is false.

It is important to realize that in conditional reasoning, and in all forms of deductive reasoning, the validity of an inference does not depend on whether the premises and the conclusion are actually (in the �real world�) true or false. All that matters is whether it is possible to conceive of a situation in which the conclusion would be false and all of the premises would be true. Indeed, there are valid inferences in which one or more of the premises and the conclusion are actually false:

Either the current pope is married or he is a divorc�. The current pope is not a divorc�. Therefore, the current pope is married.

This inference is valid because, although the premises and the conclusion are not all true, it is impossible to conceive of a situation in which all of the premises would be true but the conclusion would be false. Examples such as these demonstrate that the validity of an inference depends upon its form or structure, not on its content.

Reasoning skills are often assessed through problems involving syllogisms, which are deductive arguments consisting of two premises and a conclusion. Two kinds of syllogisms are particularly common.

In a categorical syllogism the premises and the conclusion state that some or all members of one category are or are not members of another category, as in the following examples:

All robins are birds. All birds are animals. Therefore, all robins are animals.

Some bachelors are not astronauts. All bachelors are human beings. Therefore, some human beings are not astronauts.

A linear syllogism involves a quantitative comparison in which each term displays either more of less of a particular attribute or quality, and the reasoner must draw conclusions based on the quantification. An example of a reasoning problem based on a linear syllogism is: �John is taller than Bill, and Bill is taller than Pete. Who is tallest?� Linear syllogisms can also involve negations, as in �Bill is not as tall as John.� Induction

Many aspects of problem solving involve inductive reasoning, or induction. Simply put, induction is a means of reasoning from a part to a whole, from particulars to generals, from the past to the future, or from the observed to the unobserved. Whereas valid deductive inferences guarantee the truth of their conclusions, in the sense that it is impossible for the premises to be true and the conclusion false, good inductive inferences guarantee only that, if the premises are true, the conclusion is probable, or likely to be true. There are several major kinds of inductive reasoning, including causal inference, categorical inference, and analogical inference.

In a causal inference, one reasons to the conclusion that something is, or is likely to be, the cause of something else. For example, from the fact that one hears the sound of piano music, one may infer that someone is (or was) playing a piano. But although this conclusion may be likely, it is not certain, since the sounds could have been produced by an electronic synthesizer. (See also induction, problem of.)

In a categorical inference, one makes a judgment about whether something is, or is likely to be, a member of a certain category. For example, upon seeing an animal one has never seen before, a person with a limited knowledge of dogs may be confident that what he is seeing is a dog but less certain about the specific species.

In reasoning by analogy, one applies what one has learned to another domain. Aristotle stated the formulae for two possible analogical inferences: �As A is to B, so C is to D�; and �As A is in B, so C is in D.� Analogical inference involves applying the outcomes of a known situation to a new or unknown situation. A risk in this approach, however, can occur if the two situations are too dissimilar to merit the analogous comparison. Robert J. Sternberg Other types of thinkingJudgment

A simple form of realistic thinking�i.e., thinking that is oriented toward the external environment�underlies the ability to discriminate discrete objects or items of information (e.g., distinguishing a lion from a tiger). The outcome is a judgment, and accordingly the process may be called decision making. The availability of information, the rate at which it is presented, the expectations of the person making the judgment, and the number of alternatives available influence the judgment�s accuracy and efficiency. Redundancy (or surplus) of information facilitates judgment. For example, a lion may be identified on the basis of a number of different sensory cues, such as being tan or brown, lacking stripes, having a mane, and so on. Concept attainment

A more complex form of realistic thinking underlies the ability to identify or use a class of items, as in selecting several different kinds of triangle from an array of other geometric figures. In the course of solving the problem, the individual will link together a newly experienced group of objects according to one or more of their common properties. This new grouping is then given a general name (as in first learning the meaning of the word triangle). It might also be determined that a new object fits an existing category. Physical objects are multidimensional; that is, they may vary in shape, size, colour, location (in relation to other objects), emotional significance, or connotative meaning. How a person identifies such dimensions, develops hypotheses (or tentative conclusions) about which of the specific dimensions define a class, arrives at the rules of class membership, and tests various hypotheses all reflect his ability to grasp concepts. Successful performance in all these processes leads to the formulation of pertinent rules based on one�s ability to classify specific items. (See concept formation.) Creative thinking

As discussed above, divergent (or creative) thinking is an activity that leads to new information, or previously undiscovered solutions. Some problems demand flexibility, originality, fluency, and inventiveness, especially those for which the individual must supply a unique solution. (See creativity.)

A number of processes or phases have been identified as typical of creative thinking. According to one well-known theory, in the first phase, preparation, the thinker assembles and explores resources, perhaps making preliminary decisions about their value in solving the problem at hand. Incubation represents the next phase, in which the individual mulls over possibilities and shifts from one to another relatively freely and without any rigid rational or logical preconceptions and constraints. Illumination occurs when resources fall into place and a definite decision is reached about the result or solution. Next is verification (refinement or polishing), the process of making relatively minor modifications in committing ideas to final form. Often enough, objective standards for judging creative activity (e.g., musical composition) are lacking, especially if the emotional satisfaction of the creator is an important criterion. Although the four phases have been ordered in a logical sequence, they often vary widely and proceed in different orders from one person to the next. Many creative people attain their goals by following special strategies that are not neatly describable.

The phases of preparation, incubation, illumination, and verification are characteristic of creative thinkers generally but do not guarantee that a worthwhile product will ensue. Results also depend on whether an individual has the necessary personality characteristics and abilities; in addition, the quality of creative thinking stems from the training of the creator. The artist who produces oil paintings needs to learn the brushing techniques basic to the task; the scientist who creates a new theory does so against a background of previous learning. Furthermore, creativity intimately blends objective and subjective processes; the successful creator learns how to release and to express his feelings and insights.

Creative thinking is a matter of using intrinsic resources to produce tangible results. This process is markedly influenced by early experience and training. Thus, school and work situations that encourage individual expression and that tolerate idiosyncratic or unorthodox thinking seem to foster the development of creativity. W. Edgar Vinacke