of wood are made one by glue; and a line, even if it is bent, is called one if it is continuous, as each part of the body is, e.g. the leg or the arm. Of these themselves, the continuous by nature are more one than the continuous by art. A thing is called continuous which has by its own nature one movement and cannot have any other; and the movement is one when it is indivisible, and indivisible in time. Those things are continuous by their own nature which are one not merely by contact; for if you put pieces of wood touching one another, you will not say these are one piece of wood or one body or one continuum of any other sort. Things, then, that are continuous in any way are called one, even if they admit of being bent, and still more those which cannot be bent, e.g. the shin or the thigh is more one than the leg, because the movement of the leg need not be one. And the straight line is more one than the bent; but that which is bent and has an angle we call both one and not one, because its movement may be either simultaneous or not simultaneous; but that of the straight line is always simultaneous, and no part of it which has magnitude[1] rests while another moves, as in the bent line.
(b) Things are called one in another sense because the substratum does not differ in kind; it does not differ[2] in the case of things whose kind is indivisible to the sense. The substratum meant is either the nearest to, or the furthest from, the final state. For, on the one hand, wine is said to be one and water is said to be one, qua indivisible in kind; and, on the other hand, all juices, e.g. oil and wine, are said to be one, and so are all things that can be melted, because the ultimate substratum of all is the same; for all of these are water or air.
(c) Those things are called one whose genus is one though distinguished by opposite differentiae; and these are all called one because the genus which underlies the differentiae is one (e.g. horse, man, and dog are one, because all are animals), and in a way similar to that in which the matter is one.[3]
