Vocal sound falls into two divisions according as it is animate or inanimate. The voice of living things is animate sound; notes of instruments and noises are inanimate. And of the animate voice part is articulate, part inarticulate, that of men being articulate speech, that of the animals inarticulate. Thus vocal sound is either animate or inanimate. Whatever exists is either divisible or indivisible. Of divisible things some are divisible into similar and others into dissimilar parts. Those things are indivisible which cannot be divided and are not compounded of elements, for example, the unit, the point and the musical note ; whereas those which have constituent parts, for instance, syllables, concords in music, animals, water, gold, are divisible. If they are composed of similar parts, so that the whole does not differ from the part except in bulk, as water, gold and all that is fusible, and the like, then they are termed homogeneous. But whatever is composed of dissimilar parts, as a house and the like, is termed heterogeneous. Thus all things whatever are either divisible or indivisible, and of those which are divisible some are homogeneous, others heterogeneous in their parts. Of existing things some are absolute and some are called relative. Things said to exist absolutely are those which need nothing else to explain them, as man, horse, and all other animals. For none of these gains by explanation. To those which are called relative belong all which stand in need of some explanation, as that which is greater than something or quicker than something, or more beautiful and the like. For the greater implies a less, and the quicker is quicker than something. Thus existing