[44] Jevons’ *Elementary Lessons in Logic*, pp. 41–43; *Pure Logic*, p. 6. See also J. S. Mill, *System of Logic*, Book I. chap. ii. section 5, and Shedden’s *Elements of Logic*, London, 1864, pp. 14, &c. Professor Robertson objects (*Mind*, vol. i. p. 210) that I confuse *singular* and *proper* names; if so, it is because I hold that the same remarks apply to proper names, which do not seem to me to differ logically from singular names. *Abstract Terms.* Comparison of objects, and analysis of the complex resemblances and differences which they present, lead us to the conception of *abstract qualities*. We learn to think of one object as not only different from another, but as differing in some particular point, such as colour, or weight, or size. We may then convert points of agreement or difference into separate objects of thought which we call qualities and denote by *abstract terms*. Thus the term *redness* means something in which a number of objects agree as to colour, and in virtue of which they are called red. Redness forms, in fact, the intensive meaning of the term red. Abstract terms are strongly distinguished from general terms by possessing only one kind of meaning; for as they denote qualities there is nothing which they cannot in addition imply. The adjective “red” is the name of red objects, but it implies the possession by them of the quality *redness*; but this latter term has one single meaning--the quality alone. Thus it arises that abstract terms are incapable of plurality. Red objects are numerically distinct each from each, and there are multitudes of such objects; but redness is a single quality which runs through all those objects, and is the same in one as it is in another. It is true that we may speak of *rednesses*, meaning different kinds or tints of redness, just as we may speak of *colours*, meaning different kinds of colours. But in distinguishing kinds, degrees, or other differences, we render the terms so far concrete. In that they are merely red there is but a single nature in red objects, and so far as things are merely coloured, colour is a single indivisible quality. Redness, so far as it is redness merely, is one and the same everywhere, and possesses absolute oneness. In virtue of this unity we acquire the power of treating all instances of such quality as we may treat any one. We possess, in short, general knowledge. *Substantial Terms.*