Book 10
5
Such, then, in number are the meanings of one: the naturally continuous, the whole, the individual, and the universal. All these are one because they are indivisible; some in motion, and others in concept or formula. But we must recognize that the questions, What sort of things are called one? and What is essential unity, and what is the formula? must not be taken to be the same.
6
One has these several meanings, and each thing to which some one of these senses applies will be one; but essential unity will have now one of these senses and now something else, which is still nearer to the term one, whereas they are nearer to its denotation . This is also true of element and cause, supposing that one had to explain them both by exhibiting concrete examples and by giving a definition of the term.
7
There is a sense in which fire is an element (and no doubt so too is the indeterminateThe reference is undoubtedly to Anaximander. or some other similar thing, of its own nature), and there is a sense in which it is not; because to be fire and to be an element are not the same. It is as a concrete thing and as a stuff that fire is an element; but the term element denotes that it has this attribute: that something is made of it as a primary constituent.
8
The same is true of cause or one and all other such terms.
8
Hence to be one means to be indivisible (being essentially a particular thing, distinct and separate in place or form or thought), or to be whole and indivisible; but especially to be the first measure of each kind, and above all of quantity; for it is from this that it has been extended to the other categories.
9
Measure is that by which quantity is known, and quantity qua quantity is known either by unity or by number, and all number is known by unity. Therefore all quantity qua quantity is known by unity, and that by which quantities are primarily known is absolute unity.
