18. All the questions we have asked show that we doubtless must seek to discover the differences of the various (beings), so as to distinguish them from each other; but that it is as impossible as it is unreasonable to inquire what are the differences of the differences themselves.[408] Being of beings, quantities of quantities, qualities of qualities, differences of differences cannot be discovered; but we should, wherever possible, classify exterior objects, either according to their effects, or according to salient characteristics. When this is impossible, objects should be distinguished, as for instance dark from light green.
But how is white distinguished from black? Sensation or intelligence tell us that those things are different without informing us of their reason; either sensation, because its function is not to set forth the reason of things, but only to bring them somehow to our attention; or intelligence, because it discerns things that are simple by intuition, without having to resort to ratiocination, and limits itself to the statement that something is such or such. Besides, in each one of the operations of intelligence there is a difference (a special distinctive characteristic) which enables it to distinguish different things, without this difference (which is proper to each of the operations of intelligence) itself having need to be discerned by the help of some other difference.
SOME QUALITIES ARE DIFFERENCES.
Are all qualities differences, or not? Whiteness, colors, qualities perceived by touch and taste, may become differences between different objects, though they themselves be species. But how do the sciences of grammar or of music constitute differences? The science of grammar renders the mind grammatical, and the science of music renders the mind musical, especially if they be untaught; and these thus become specific differences. Besides, we have to consider whether a difference be drawn from the same genus (from which the considered things are drawn), or from some other genus. If it be drawn from the same genus, it fulfils, for the things of this genus, the same function as does a quality to the quality to which it serves as difference. Such are virtue and vice; virtue is a particular habit, and vice is also a particular habit; consequently, as habits are qualities, the differences of these habits (either of virtue or vice) will be qualities. It may perhaps be objected that a habit without difference is not a quality, and that it is the difference alone which constitutes the quality.[409] We will answer that it is (commonly) said that sweet is good, and that bitter is bad; this then implies a recognition of their difference by a habit (a manner of being), and not by a quality.
What if sweet be said to be "crude," or thick and bitter, thin or refined? The answer is that coarseness does not inform us of the nature of sweetness, but indicates a manner of being of what is sweet; and similarly, with what is refined.
THERE ARE DIFFERENCES WHICH ARE NOT QUALITIES.
There remains for us to examine if a difference of a quality never be a quality, as that of a being is not a being, nor that of a quantity, a quantity. Does five differ from three by two? No: five does not differ from three, it only exceeds it by two. How indeed could five differ from three by two, when five contains two? Likewise, a movement does not differ from a movement by a movement. As to virtue and vice, here is one whole opposed to another whole, and it is thus that the wholes are distinguished. If a distinction were drawn from the same genus, that is, from quality, instead of founding itself on another genus; as, for instance, if one said that such a vice referred to pleasures, some other to anger, some other to acquisitiveness, and if one were to admit that such a classification was good; it would evidently result that there are differences that are not qualities.
VARIOUS DERIVATIVES OF THE CATEGORY OF QUALITY.
19. As has been indicated above, the genus of quality contains the (beings) which are said to be qualified (qualitative entities), inasmuch as they contain some quality (as, for instance, the handsome man, so far as he is endowed with beauty).[410] These (beings) however do not properly belong to this genus, for otherwise there would here be two categories. It suffices to reduce them to the quality which supplies their name.
So non-whiteness, if it indicate some color other than white, is a quality; if it express merely a negation, or an enumeration, it is only a word, or a term which recalls the object; if it be a word, it constitutes a movement (so far as it is produced by the vocal organ); if it be a name or a term, it constitutes, so far as it is a significative, a relative. If things be classed not only by genera, if it be admitted that each assertion and expression proclaim a genus, our answer must be that some affirm things by their mere announcement, and that others deny them. It may perhaps be best not to include negations in the same genus as things themselves, since, to avoid mingling several genera, we often do not include affirmations.