Our first presupposition must be that in nature nothing acts on, or is acted on by, any other thing at random, nor may anything come from anything else, unless we mean that it does so in virtue of a concomitant attribute. For how could ‘white’ come from ‘musical’, unless ‘musical’ happened to be an attribute of the not-white or of the black? No, ‘white’ comes from ‘not-white’ – and not from any ‘not-white’, but from black or some intermediate colour. Similarly, ‘musical’ comes to be from ‘not-musical’, but not from any thing other than musical, but from ‘unmusical’ or any intermediate state there may be.