Quality is the monadic element of the world. Anything whatever, however complex and heterogeneous, has its quality sui generis, its possibility of sensation, would our senses only respond to it.
…a quality is merely something that might be realized, while an occurrence is something that actually takes place. [—] A quality […] has no individuality. Two qualities are different only so far as they are unlike. Individuality is an aggressive unity, arising from an absolute refusal to be in any degree responsible for anything else. This a quality cannot have since it is too utterly irrespective of anything else even to deny it.
The mode of being of the quality is that of Firstness. That is to say, it is a possibility. It is related to the matter accidentally; and this relation does not change the quality at all, except that it imparts existence, that is to say, this very relation of inherence, to it.
…qualities are not, properly speaking, individuals. All the qualities you actually have ever thought of might, no doubt, be counted, since you have only been alive for a certain number of hundredths of seconds, and it requires more than a hundredth of a second actually to have any thought. But all the qualities, any one of which you readily can think of, are certainly innumerable; and all that might be thought of exceed, I am convinced, all multitude whatsoever. For they are mere logical possibilities, and possibilities are general, and no multitude can exhaust the narrowest kind of a general. Nevertheless, within limitations, which include most ordinary purposes, qualities may be treated as individuals. At any rate, however, they form an entirely different universe of existence. It is a universe of logical possibility.