  We want group (a) to correspond to the category ‘substance’. Unfortunately, the Vaiśeṣikas claim that wholes are distinct from, and inhere in, their parts. The only substances which do not inhere in anything are the atomic substances (which for the Vaiśeṣikas correspond with the eternal substances). Group (c) corresponds to the category ‘universal’, for universals are said to inhere in things (substances, qualities and motions) but do not have anything inhering in them. Group (b) comprises, the non-atomic substances, the qualities and the motions. Let us now divide this group into two: those which are inhered in only by universals, and those which are inhered in by other things as well. The former corresponds to the categories ‘quality’ and ‘motion’, for substances are inhered in, not only by universals, but also by qualities, motions, as well as by other substances. Finally, we must find a way to sub-divide the former group into qualities and motions. More traditional Naiyāyikas preserve the distinction by saying that motions, but not qualities, cause the substances in which they inhere to come into contact with (or break away from) each other. This, however, appeals to the idea of ‘contact’, which cannot itself be defined in terms of our primitive relation inherence. Some radical Naiyāyikas (especially Bhāsaravajña) claim that motions are just a kind of quality, as their properties are so similar. The only remaining category is ‘differentium’ (viśeṣa), whose members reside in and individuate the eternal substances i.e. the atoms. The point, perhaps, is that all other things are individuated by the universals and wholes that inhere in them, but two atoms of the same substance are in all respects identical. But if objects are individuated by means of what inheres in them, then there must be something inhering in each atom which distinguishes it from the others—a ‘differentium’ (see §10.2).