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prophetic power of more or less probability. Having observed that many substances assume, like water and mercury, the three states of solid, liquid, and gas, and having assured ourselves by frequent trial that the greater the means possess of heating and cooling, the more substances we can vaporise and freeze, we pass confidently in advance of fact, and assume that all substances are capable of these three forms. Such a generalisation was accepted by Lavoisier and Laplace before many of the corroborative facts now in our possession were known. The reduction of a single comet beneath the sway of gravity was considered sufficient indication that all comets obey the same power. doubted that the law of gravity extended over the whole heavens ; certainly the fact that a few stars out of many millions manifest the action of gravity, is now held to be sufficient evidence of its general extension over the visible universe

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232. l. From Fleming's Vocabulary of Philosophy, ed. 1858, pp. 91–92.

Montesquieu observed very justly, that in their classification of the citizens, the great legislators of antiquity made the greatest display of their powers, and even soared above themselves.” Burke, On the French Revolution.

" A class consists of several things coming under a common description." Whately, Log., b. i., g 3.

“ The sorting of a multitude of things into parcels, for the sake of knowing them better, and remembering them more easily, is classification. When we attempt to classify a multitude of things, we first observe some respects in which they differ from each other ; for we could not classify things that are entirely alike ; as, for instance, a bushel of peas ; we then separate things that are not alike, and bring together things that are similar." Taylor, Elements of Thought.

“ In every act of classification, two steps must be taken ; certain marks are to be selected, the possession of which is to be the title to admis

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sion into the class, and then all the objects that possess them are to be ascertained. When the marks selected are really important and connected closely with the nature and functions of the thing, the classification is said to be natural;. where they are such as do not affect the nature of the objects materially, and belong in common to things the most different in their main properties, it is artificial.” Thomson, Outline of Laws of Thought, 2d edit., p. 377.

The condition common to both modes of clas. sification, is to comprehend everything and to suppose nothing. But the rules for a natural classification are more strict than for an artificial or arbitrary one. may classify objects arbitrarily in any point of view in which we are pleased to regard them. But a natural classification can only proceed according to the real nature and qualities of the objects. The advantages of classification are to give a convenient form to our acquirements, and to enlarge our knowledge of the relations in which different objects stand to one another. A good classification should—1st, Rest on one principle or analogous principles. 2d, The principle or principles should be of a constant and permanent character. 3d, It should be natural, that is, even when artificial, it should not be violent or forced. 4th, It should clearly and easily apply to all the objects classified.

The principles on which classification rests are these :—1st, of Generalization; 2d, of Specification; and 3d, of Continuity.


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Classification proceeds upon observed resem. blances. Generalization rests upon the principle, that the same or similar causes will produce similar effects.-Mill, Log., b. i., chap. 7, § 4; McCosh, Typical Forms, b. iii., chap. 1.

2. From Jevons' Elementary Lessons in Logic, ed. 1878, pp. 276–286. It may

be said that the subject we are treating is coextensive with the science of logic. All thought, all reasoning, so far as it deals with general names or ge::eral notions, may be said to consist in classification. Every common name or general name is the name of a class, and every name of a class is a common “ Metal” is the name of one class of substantives so often used in our syllogistic examples ; “ Element of another class, of which the former class is part. Reasoning has been plausibly represented to consist in affrming of the parts of a class whatever may be affirmed of the whole. Every law of nature which we arrive at enables us to classify together a number of facts, and it would hardly be too much to define logic as the theory of classification.

Classification may perhaps be best defined as the arrangement of things, or our notions of them, according to their resemblances, or identities.

Every class should so be constituted as to contain objects exactly resembling each other in certain definite qualities, which are stated in the definition of the class. The more numerous and extensive the resemblances which are thus indicated by any system of classes, the more perfect and useful must that system be considered.

Mr. Mill thus describes his view of the mean. ing—“Classification is a contrivance for the best possible ordering of the ideas of objects in our minds ; for causing the ideas to accompany or succeed one another in such a way as shall give us the greatest command over our knowledge already acquired, and lead most directly to the acquisition of more. The general problem of classification, in reference to these purposes may be stated as follows : To provide that things shall be thought of in such groups, and those groups in such an order, as will best conduce to the remembrance, and to the ascertainment of their


A collection of objects may be classified in an indefinite number of ways... Any quality which is possessed by some and not by others


be taken as the first difference, and the


thus distinguished may be subdivided in succession by any other qualities taken at will. Thus a library of books might be arranged, (1) according to size, (2) according to the language in which they are written, 3) according to the alphabetic order of their authors' names, (4) according to their subjects ; and in various other ways. In large libraries and in catalogues such modes of arrangement are adopted and variously combined. ... The population of a kingdom, again,

. may be classified in an almost endless number of ways with regard to different purposes or sci

The population of the Ūnited Kingdom


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