 With regard to body, Cordemoy warns that we must be careful to avoid the mistake made by other Cartesians, who have conflated what are in fact two distinct things, namely, ‘bodies’ and ‘matter’. The former are, according to Cordemoy, the true extended substances, while the latter are assemblages, or collections, of the former. The key point is that as substances, bodies must be simple: if bodies had parts, they would depend on those parts to be what they are, and in this way the parts would threaten a body’s very status as a substance. Thus we are led to atomism on strictly a priori grounds: in positing bodies as substances, we are precluded from attributing parts to them, for if we did, they would no longer be substances. Matter on this account is divisible not because its nature is extension and any extension can always be divided, but rather because it is composed of bodies which can be separated from each other, though each one is itself indivisible.