BLTC Press Titles


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Further Adventures of an Irish R. M.

Edith Somerville and Martin Ross


The Characters of Theophrastus

Theophrastus


Some Experiences of an Irish R. M.

Edith Somerville and Martin Ross


Knowledge of Higher Worlds and its Attainment

Rudolf Steiner


Elementary lessons in logic

by William Stanley Jevons

Excerpt:

Metals,

Elementary substances.

Iron is one of the metals, and metals are elements or simple undecomposable substances, in the sense of being among them or a part of them, but not as composing the whole. It follows necessarily that "Iron is one of the elementary substances." We have had then two exam-, pies of a fixed and necessary form of thought which is necessary and true whatever the things may be to which it is applied. The form of argument may be expressed in several different ways, and we shall have to consider it minutely in the lessons on the syllogism; we may express it, for instance, by saying that "part of a part is part of the whole." Iron is part of the class of metals, which is part of the class of elements: hence iron is part of the class of elements.

If I now introduce another definition of Logic and say that it is "the science of the necessary forms of thought," the reader will I hope clearly apprehend the meaning of the expression "necessary forms of thought." A form is something which may remain uniform and unaltered, while the matter thrown into that form may be varied. Medals struck from the same dies have exactly the same form, but they may be of various matter, as bronze, copper, gold or silver. A building of exactly the same form might be constructed either of stone or bricks; furniture of exactly similar shape may be made of oak, mahogany, walnut wood, etc. Just as we thus familiarly recognize the difference of form and substance in common tangible things, so we may observe in Logic, that the form of an argument is one thing, quite distinct from the various subjects or matter which may be treated in that form. We may almost exhibit to the eye the form of reasoning to which belong our two latter arguments, as follows:— lt,l

... (T) \.

**A») * b* * *.

If within the three pairs of brackets, marked respectively X, Y and Z we. place three names, such that the one in place of X may he said to come under that in Y, and that in Y under that in Z, then it necessarily follows that the first (X) comes under the last (Z).

Logic, then, is the science occupied in ascertaining and describing all the general forms of thought which we must employ so long as we reason validly. These forms are very numerous, although the principles on which they are constructed are few and simple. It will hence appear that logic is the most general of all the sciences. Its aid must be more often required than the aid of any other science, because all the particular sciences treat portions only of existing things, and create very different and often unconnected branches of knowledge. But logic treats of those principles and forms of thought which must be employed in every branch of knowledge. It treats of the very origin and foundations of knowledge itself; and though it is true that the logical method employed in one science may differ somewhat from that employed in another science, yet whatever the particular form may be, it must be logical, and must conform to the laws of thought. There is in short something in which all sciences must be similar; to which they must conform so long as they maintain what is true and selfconsistent; and the work of logic is to explain this common basis of all science.

One name which has been given to Logic, namely the Science of Sciences, very aptly describes the all extensive power of logical principles. The cultivators of special branches of knowledge appear to have been fully aware of the allegiance they owe to the highest of the sciences, for they have usually given names implying this allegiance. The very name of logic occurs as part of nearly all the names recently adopted for the sciences, which are. often vulgarly called the "ologies," but are really the "logics," the "o" being only a connecting vowel or part of the previous word. Thus geology is logic applied to . explain the formation of the earth's crust; biology is logic applied to the phenomena of life; psychology is logic applied to the nature of the mind; and the same is the case with physiology, entomology, zoology, teratology, morphology, anthropology, theology, ecclesiology, thalattology, and the rest*. Each science is thus distinctlyconfessed to be a special logic. The name of logic itself, is derived from the common Greek word Xoyos, which usually means word, or the sign and outward manifestation of any inward thought. But the same word was also used to denote the inward thought or reasoning of which words are the expression, and it is thus probably that later Greek writers on reasoning were led to call their science


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