Introduction to Logical Theory [antikvár]

PREFACEthere are in existence many text-books and technical treatises on formal logic, and I have not sought in this book to add to their number. Many such books, excellent as they often are in their expositions of the technical and systematic aspects of logic, deal comparatively sketchily, and often rather mis-leadingly, with the relations between the formal systems they expound and the logical features of ordinary discourse. As a result of this omission, the true character of formal logic itself is apt to be left obscure. So this book has two complementary aims : one is to bring out some points of contrast and of contact between the behaviour of words in ordinary speech and the behaviour of symbols in a logical system; the other is to make clear, at an introductory level, the nature of formal logic itself. I have included enough of the elementary material of formal logic to provide a basis for the philosophical discussion of its nature, and to serve, if desired, as an introduction to more advanced technical treatises. Since the book is designed to be used as a general introduction to logic, I have added a concluding chapter on induction and probability.I wish to acknowledge my great indebtedness to the many Oxford colleagues from whose discussions of the topics of this book I have profited; and among these, in particular, to Mr. H. P. Grice, from whom I have never ceased to learn about logic since he was my tutor in the subject; and to Professor Gilbert Ryle, Mr. G. A. Paul and Miss Ruby Meager, all of whom read the book either in manuscript or in proof and saved me from many inelegancies and mistakes.P. F. S.Oxford, May, 1952.chapter 1LOGICAL APPRAISAL1. when a man says or writes something, there are many different ways in which his performance may be judged. Among other things, we may question his truthfulness or criticize his style, we may assess the morality of what he says, or we may appraise its logic; though not all these types of assessment are appropriate to all kinds of utterance. The words 4 logical' and f illogical' are themselves among the words of logical appraisal. If you call a discourse logical, you are in some degree commending it. If you call it illogical, you are, so far, condemning it. Words and phrases which go with * logical' are 4 consistent ',4 cogent', 4 valid 4 it follows '; words and phrases which go with 4 illogical' are 4 inconsistent4 self-contra-dictory 4 invalid 4 a non sequitur Part of our problem is to see what sort of appraisal these words are used for, to what kind of standards we appeal in using them. It is easy to see that these are not moral or aesthetic standards; that logical criticism is not, say, a kind of literary criticism. A slightly more difficult distinction is that between the criticism we offer when we declare a man's remarks to be untrue and the criticism we offer when we declare them to be inconsistent. In the first case we criticize his remarks on the ground that they fail to square with the facts; in the second case we criticize them on the ground that they fail to square with one another. The charge of untruth refers beyond the words and sentences the man uses to that in the world about which he talks. We deny his assertion, and, in doing so, make a counter-assertion of our own about the subject of his discourse. We contradict him. But the charge of inconsistency does not in this way refer to anything outside the statements that the man makes. We simply consider the way his statements hang together. Just from considering the sentences themselves, as they are used, we can, perhaps, see that not all the statements he makes can be true together. It is not that we contradict him, and in doing so, make a counter-assertion about the subject of his remarks j1