Individuation, - is the unity of a thing with itself, or that whereby a thing is what it is.

To begin with those species of body that are not properly organized, which have neither life nor sense, as stones, metals, etc. In these, individuation seems to consist in nothing but greater or less: take the less part of a stone away, you may still call it the same stone; take an equal part with the remains, that individuation ceases, and they are two new individuals. Divide a stone, etc. as often as you please, every part of it will be a stone still, another individual stone, as much as any in the mountain or quarry out of which it was first cut, even though reduced to the minutest sand, or, if possible, a thousand times less. But when we take one step farther, and proceed a degree higher, to the vegetable kingdom, the case is far otherwise; and indeed Nature seems to be still more distinct, and, as it were, careful in its individuation, the higher it rises, till at last it brings us to that great transcendental individual, the only proper uncompounded essence, the One God, blessed for ever.

To return to plants: their individuation consists in that singular form, contexture, and order of their parts, whereby they are disposed for those uses to which Nature has designed them, and by which they receive and maintain their beings For example, in a tree, though you take away the branches, it grows, receives nourishment from the earth, maintains itself, and is still a tree, which the parts thereof are not when separated from the rest; for we cannot say that every part of a tree is a tree, as we can that every part of a stone is still a stone, but if this tree be cloven in two or more pieces, or felled by the roots, this contexture, or orderly respect of the parts one to another, ceases; its essence as a tree is destroyed; its individuation perishes; and it is no more a tree, but a stump, or piece of timber.

Let us proceed a degree higher, to merely sensible creatures, who are not so immediately depending on the earth, the common mother, as the plants, nor rooted to it as they are, but walk about, and have a kind of independent existence, and are a sort of world by themselves. And here the individuation consists in such a particular contexture of their essential parts, and their relation one toward another, as enables them to exert the operations of the sensible or animal life. Thus, cut off the legs or any other parts of an animal, it is the same animal still; but cut off its head, or take away its life, and it is no longer that individual animal, but a mere carcase, and will, by degrees, resolve itself into common matter again.

To ascend now to the highest rank of visible beings, - the rational. The individuation of man appears to consist in the union of a rational soul with any convenient portion of fitly organized matter. Any portion of matter duly qualified, and united to the soul by such a union as we experience, is immediately individuated by it, and, together with that soul, makes a man; so that, if it were possible for one soul to be clothed over and over at different times with all the matter in the universe, it would in all those distinct shapes be the same individual man. Nor can a man be supposed in this case to differ more from himself, than he does from what he really was when an infant, or just passed an embryo, when compared with what he is when of adult or decrepit age; he having, during that intermediate time, changed his portion of matter over and over; as, being fat and lean, sick and well, having been exhausted by bleeding, effluvia, perspiration, etc.; and reunited again by aliment; so that perhaps not one particle, or but very few of the first matter which he took from his parents, and brought with him into the world, is now remaining.