  The Vaiśeṣika traditionally and uniquely accept into their ontology a category of item called ‘basic differentia’ (viśeṣa), from which, some claim, they derive their name. The Manual of Reason defines these items as follows (TS 83): “those entities which reside in the eternal substances [i.e. the atoms] and function as their differentiators are called viśeṣa”. The idea is that, just as a cow and a horse are distinct entities, as they have distinct properties, so too even two atoms of the same substance, e.g. earth, must differ with respect to at least one property. Each atom, therefore, possesses a ‘differentium’ unique to itself, which serves to distinguish it from any other atom of the same type. The assumption, then, is that any two non-identical items are distinguished by virtue of possessing distinct properties. This is the contraposed version of Leibniz’ Law that Indiscernibles are Identical, that (∀P)(Px ≡ Py) → (x = y), where “P” ranges over properties. The principle faces triviality unless certain constraints are placed on the range of properties quantified over. For example, if the property “… = y” is permitted, the principle states vacuously that identicals are identical. The Vaiśeṣikas implicitly restrict the principle to intrinsic, non-relational properties of the objects concerned, ruling out, for example, ‘being at a certain spatial or temporal location’ as being a property capable of discriminating two otherwise identical objects. Thus, the claim seems to be that no two objects, including atoms, can be intrinsically identical. This is how Leibniz himself appears to have understood his Law, saying that “It is always necessary that beside the difference of time and place there be internal principles of distinction….thus although time and place serve in distinguishing things, we do not easily distinguish them by themselves,” and that “There is no such thing as two individuals indiscernible from each other. Two drops of water, or milk, viewed with a microscope, will appear distinguishable from each other”.