We are indebted to Professor Dewey, for an analysis of the thought process. Every instance of thinking reveals five steps:
(1) A felt difficulty, (2) its location and definition, (3) suggestions of possible solutions, (4) development by reasoning of the bearings of the most promising suggestion, (5) further observation or experiment leading to its acceptance or rejection, that is a conclusion either of belief or disbelief.
When instinct or habit suffices to adjust us to our environment, action runs along smoothly, freely, uninterruptedly. In consequence the provocation to thinking may at first be a mere vague shock or disturbance. We are, as it were, in trouble without knowing precisely what the trouble is. We must carefully inquire into the nature of the problem before undertaking a solution. To take a simple instance, an automobile may suddenly stop. We know there is a difficulty, but whether it is a difficulty with the transmission, with the carburetor, or with the supply of gasoline, we cannot at first tell. Before we do anything else in solving our problem, we find out literally and precisely what the trouble is. To take a different situation, a doctor does not undertake to prescribe for a patient until he has diagnosed the difficulty, found out precisely what the features of the problem are.
The second step after the situation has been examined and its precise elements defined, is suggestion. That is, we consider the various possibilities which suggest themselves as solutions to our problem. There may be several ways of temporarily repairing our engine; the doctor may think of two or three possible treatments for a disease. In one sense, suggestion is uncontrollable. The kind of suggestions that occur to an individual depend on his "genius or temperament," on his past experiences, on his hopes or fears or expectations when that particular situation occurs. We can, however, through the methods of science, control suggestions indirectly. We can do this, in the first place, by reëxamining the facts which give rise to suggestion. If upon close examination, the facts appear differently from what they did at first, we will derive different inferences from them. Different suggestions will arise from the facts A, B, C, than from the facts A', B', C'. Again we can regulate the conditions under which credence is given to the various suggestions that arise. These suggestions are entertained merely as tentative, and are not accepted until experimentally verified. "The suggested conclusion as only tentatively entertained constitutes an idea."
After the variety of suggestions that proffer themselves as solutions to a problem have been considered, the third step is the logical development of the idea or suggestion that gives most promise of solving the difficulty. That is, even before further facts are sought, the idea that gives promise of being a solution is followed out to its logical consequences. Thus, for example, astronomers were for a long time puzzled by unexplained perturbations in the path of the planet Uranus. The suggestion occurred that an unseen planet was deflecting it from the path it should, from observation and calculation, be following. If this were the case, from the amount of deflection it was mathematically calculated, prior to any further observation, that the supposed planet should appear at a certain point in space. It was by this deductive elaboration that the planet Neptune was discovered. It was figured out deductively that a planet deflecting the path of the planet Uranus by just so-and-so much should be found at just such and such a particular point in the heavens. When the telescopes were turned in that direction, the planet Neptune was discovered at precisely the point deductively forecast.
The elaboration of an idea through reasoning it out may sometimes lead to its rejection. But in thinking out its details we may for the first time note its appositeness to the solution of the problem in hand. The gross suggestion may seem wild and absurd, but when its bearings and consequences are logically developed there may be some item in the development which dovetails into the problem as its solution. William James gives as the outstanding feature of reasoning, "sagacity, or the perception of the essence."[1] By this he meant the ability to single out of a complex situation or idea the significant or key feature. It is only by a logical development of a suggested solution to a problem that it is possible to hit upon the essence of the matter for a particular situation, to single out of a gross total situation, the key to the phenomenon. "In reasoning, A may suggest B; but B, instead of being an idea which is simply obeyed by us, is an idea which suggests the distinct additional idea C. And where the train of suggestion is one of reasoning distinctively so-called as contrasted with mere 'revery,' ... the ideas bear certain inward relations to each other which we must carefully examine. The result C yielded by a true act of reasoning is apt to be a thing voluntarily sought, such as the means to a proposed end, the ground for an observed effect, or the effect of an assumed cause."[2] Thus what at first sight might seem a fantastic suggestion may, when its bearings are logically followed out, be seen in one of its aspects to be the key to the solution of a problem. To primitive man it might have seemed absurd to suggest that flowing water might be used as power; to the man in Franklin's day that the same force that was exhibited in the lightning might be used in transportation and in lighting houses.[1]
[Footnote 1: James: Psychology, vol. II, p. 343.]
[Footnote 2: Ibid., p. 329.]
[Footnote 1: James gives an illuminating passage on the importance of the effectiveness of reasoning things out: "I have a student's lamp, of which the flame vibrates most unpleasantly unless the collar which bears the chimney be raised about a sixteenth of an inch. I learned the remedy after much torment by accident, and now always keep the collar up with a small wedge. But my procedure is a mere association of two totals, diseased object and remedy. One learned in pneumatics could have named the cause of the disease, and thence inferred the remedy immediately. By many measurements of triangles, one might find their area always equal to their height multiplied by half their base, and one might formulate an empirical law to that effect. But a reasoner saves himself all this trouble, by seeing that it is the essence (pro hac vice) of a triangle to be the half of a parallelogram whose area is the height into the entire base. To see this he must invent additional lines; and the geometer must often draw such to get at the essential properties he may require in a figure. The essence consists in some relation of the figure to the new lines, a relation not obvious at all until they are put in. The geometer's sagacity lies in the invention of the new lines." (Psychology, vol. II, pp. 339-40.)]
But no thinking is conclusive until after the experimental certification and warranting of the idea which has been held in mind as the solution of the problem. By deduction, by logical elaboration of an idea, we find its adoption involves certain consequences. Some of the logical consequences which follow from an idea may indicate that it is a plausible solution of our problem. But no matter how plausible a suggestion looks, until it is verified by observation or experiment the thinking process is not concluded, is not finished, as we say, conclusively. When an idea or a suggestion has been developed, and seen to involve—as an idea—certain inevitable logical consequences, the idea must be tested by further observation and experiment. Suggestions arise from facts and must be tested by them. Until the suggestion is verified, it remains merely a suggestion, a theory, a hypothesis, an idea. It is only when the consequences implied logically in the very idea itself are found in the actual situation that the idea is accepted as a solution to the problem. Sometimes the suggestion may be verified by observation; sometimes conditions must be deliberately arranged for testing its adequacy. In either case it is only when the facts of the situation correspond to the conditions theoretically involved that the tentative idea is accepted as a conclusion.