Logic - Deductive and Inductive by Carveth Read
page 43 of 478 (08%)
page 43 of 478 (08%)
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affairs are without logical criteria; that Logic must be confined to
symbols, and considered entirely as mental gymnastics. In this book prominence will be given to the character of Logic as a formal science, and it will also be shown that Induction itself may be treated formally; but it will be assumed that logical forms are valuable as representing the actual relations of natural and social phenomena. § 7. Symbols are often used in Logic instead of concrete terms, not only in Symbolic Logic where the science is treated algebraically (as by Dr. Venn in his _Symbolic Logic_), but in ordinary manuals; so that it may be well to explain the use of them before going further. It is a common and convenient practice to illustrate logical doctrines by examples: to show what is meant by a Proposition we may give _salt is soluble_, or _water rusts iron:_ the copulative exponible is exemplified by _salt is savoury and wholesome_; and so on. But this procedure has some disadvantages: it is often cumbrous; and it may distract the reader's attention from the point to be explained by exciting his interest in the special fact of the illustration. Clearly, too, so far as Logic is formal, no particular matter of fact can adequately illustrate any of its doctrines. Accordingly, writers on Logic employ letters of the alphabet instead of concrete terms, (say) _X_ instead of _salt_ or instead of _iron_, and (say) _Y_ instead of _soluble_ or instead of _rusted by water_; and then a proposition may be represented by _X is Y_. It is still more usual to represent a proposition by _S is (or is not) P, S_ being the initial of Subject and _P_ of Predicate; though this has the drawback that if we argue--_S is P_, therefore _P is S_, the symbols in the latter proposition no longer have the same significance, since the former subject is now the predicate. |
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