EXTENSION, in logic, is a word put into contrast with another term, COMPREHENSION, and the two mutually explain each other. A general notion is said to be extensive according to the extent of its application, or the number of objects included under it. Thus, figure is a term of very great extension, because it contains in its compass many varieties, such as round, square, oblong, polygonal. etc. In like manner, European is more extensive than German, man than European, animal than man, organized being than animal. The highest genera are formed by taking in a wider range of objects. Matter and mind are the most extensive classes that we can form. For, although a higher genus is sometimes spoken of, viz., existence; to call this a class is to generalize beyond real knowledge, which does not begin till we have at least two actual things to contrast with each other. What can be contrasted only with non-existence, non entity. or nothingness, is not genuine knowledge: no property can be affirmed of it apart from the thing itself. Matter, in its contrast to mind, is a real cognition; and rice versa, mind in its contrast to matter. These, then, are the most extensive terms that have any real knowledge attached to them. But this property of E. is
gained by dropping more and more of the peculiarities of the included individuals; "Organized being," in order to include both plants and animals, must drop from its signification what is peculiar to each, and mean only what is common to both. In short, these very extensive notions have a very narrow signification; it is the less exten sive that have most meaning. The meaning of "man," or the number of attributes implied in this generic expression, is large. Everything that goes to a human being— the human form and organization, the mental attributes of reason, speech, etc.—is expressed by this term, which is on that account said to be more COMPREHENSIVE than animal or organized being. Thus it may be seen that the greater the E., the less is the comprehension; and the greater the comprehension, the less is the extension. An individual name is the term of greatest comprehension, and of least extension. " Socrates" comprehends all that is common to men and to philosophers, together with all that is peculiar to himself. On the logical uses of this distinction, see sir W. Hamil ton's Lectures on Logic, i. 140.