4o8 THE POPULAR SCIENCE MONTHLY 



objects in question are wholly under our control, so that in dealing with 

 them we have no " course of experience/' to use Charles Peirce's phrase, 

 that is, no series of experiences which we have passively to await to see 

 what they are, but are guided wholly by our own control, and are dealing 

 wholly with objects which are what we make them. A given set of 

 premises we construct in terms of symbols, diagrams, or figures, hereby 

 expressing the meaning of these premises. Our deduction consists 

 of the reading of this meaning from a new point of view. The fecundity 

 of the process depends upon our power to combine at pleasure various 

 constructions in various permitted orders and syntheses. The precise 

 relation between such arbitrary objects, and the objects of ordinary 

 experience, forms a topic of almost inexhaustible interest to the student 

 both of logic and of the mental processes concerned. 



I have thus indicated that the problems of the psychology of deduc- 

 tion have thus far hardly been attacked, mainly because psychologists 

 have usually been so little interested in live deduction as it exists in 

 mathematical science. So long as the myth still exists in text-books, 

 that deduction is adequately to be represented by the form of the 

 syllogism and the interpretation of that form which Professor Pillsbury 

 cites and uses ; so long as it is imagined that deduction merely lets out 

 of the bag the cat that has already been put in it, our logic will languish 

 and our psychology of reasoning will fail to fulfil the purposes of 

 pragmatism or of any other doctrine of the reasoning process. So long 

 as it is supposed that the main purpose of deduction is to produce 

 belief in the conclusions, the psychology of certain of the most important 

 human thinking processes must be lost. As a fact all tolerance, all 

 considerateness in advance of action, all deliberate working out of ideal 

 consequences of modes of behavior concerning which we deliberate, — all 

 such processes would be impossible. A great deal of toleration depends 

 upon seeing how my opponent's conclusions are related to his premises, 

 although I may have no belief either in his premises or in his conclu- 

 sions. The process of deduction, in case of a practical deliberation con- 

 cerning what it is best to do, helps us because we thereby learn in advance 

 what would be the case if so and so were done, even if we ourselves have 

 no tendency whatever as yet to decide in favor of the hypothetical course 

 of procedure. 



It seems to me then that the fecundity of the deductive process, 

 the essence of the ideal experiment, and the genuine use of deduction, 

 where it is not intended to produce belief but to give us insight into a 

 connection of premises and conclusion, should form the topic of psycho- 

 logical studies such as tlnis far have attracted small attention. 



