The defining property of an individual is that there is just that one thing that is that individual. Thus, if an individual also belongs various kinds of things, as most or all things do, then it is distinguished in some way by being the one thing that has, next to its properties and relations that are characteristic of the kinds it belongs to, some properties and relations that distinguish it as that unique thing, and none other.

It is an interesting fact that for the human mind everything is of some kind, and that quite often, and in spite of the fact that every human being knows or supposes himself or herself to be a unique individual, it is not easy at all to say what uniquely distinguishes something apart from temporal and spatial coordinates. The Scholastics phrased this difficulty as "individuum ineffabile est" - what is (truly) individual cannot be (adequately) expressed, which is not to say it cannot be individually characterized, but rather that there is more to individuals than can be said about them, and perhaps also that it is the unsayable part is or contains the individually essential part.

This is true in so far as one's mind, self or brain is and contains and can do far more than one can experience at any time, or can be conscious of. There is more to anyone than is given in one's experience.