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Leffingwell Professor of Philosophy in the College for Women of

Western Reserve University

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Copyright, 1902,





The deductive part of this book may require a few words of explanation.

In most text-books on logic deduction and induction are treated from two very different standpoints. Induction is regarded as a means for the investigation of nature, and its canons are frankly objective or material'. They tell us how things must be related to each other in one respect if they are also related in some other respect (e.g., how two events must be related in time if one is the cause of the other); and they do not say anything about the relation of our thoughts to each other as mere thoughts, or give any rules for the arrangement and manipulation of the words in which these thoughts are expressed.

Deduction, on the other hand, is usually defined as the “ science of the laws of thought”—as one writer says, its “ object-matter is thought”, —and it is treated altogether from the subjective or formal' standpoint, as though mere thoughts as such could be consistent or inconsistent, wholly regardless of the nature of the object to which they refer; and then, when it comes to working out the details of the subject from this standpoint, the laws of thought' are treated practically as though they were laws for the right arrangement and manipulation of words. Hence we have rules of the syllogism and allied rules for conversion and obversion which say nothing whatever about the things under discussion and their relations to each other, but tell us only how we must or must not arrange our words in discussing them. 101649


In this book I have tried to treat deduction from the objective standpoint that everybody assumes in the treatment of induction. Consequently I have omitted the traditional rules of the syllogism and put in their place a direct statement of the principles on which we reason in the different figures, adding certain cautions' that must be observed if the principles are not to be misapplied; and I have treated conversion and obversion in much the same way.

The fourth figure of the syllogism seemed to me not to represent any distinct principle of reasoning, and therefore to have no proper place in the objective treatment of logic; but I have explained the traditional way of dealing with it. The 'algebra' of logic I have omitted altogether. Readers interested in it are referred to the “ Johns Hopkins Studies in Logic” (Little, Brown & Co., Boston).

However imperfect my own treatment of deduction from the objective standpoint may be, I believe that the standpoint itself is not only more correct philosophically than the subjective, but also better pedagogically; for we do far more to make a student clear-headed by teaching him to look a situation in the face and analyze it than by giving him any amount of dexterity in the reduction of arguments to a given verbal form.

My indebtedness to other authors is apparent. less indebted to individuals—particularly to colleagues in other departments who have given me valuable suggestions on matters related to their special subjects; but most of all to Dr. W. T. Marvin, to whom I read the whole book while it was still in manuscript.

H. A. A. March 21, 1902.

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