The Principles of Science: A Treatise on Logic and Scientific Method

Terms. Comparison of different 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 called qualities, and denoted 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 can 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 number or plurality. Red objects are numerically distinct each from each, and there are a multitude of such objects ; but redness is a single exis tence 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 dif ferent kinds of colours. But in distinguishing kinds, » J. S. Mill, 'System of Logic,' Book I. chap. ii. section 5. Jevons' 'HwBenUry Lessons in Logic,' pp. 4 '-43 ; 'Pure Logic,' p. 6. See abo Shedden's ' Elements of Logic,' London, 1 864, pp. 1 4, &c