  Nevertheless, in declaring that a substance is necessarily indivisible, Leibniz renders it impossible for a body, or matter alone, to be a substance. Thus, Cartesian corporeal substance, the essence of which is simply extension, cannot exist as substance. Put differently, Leibniz's argument is that nothing that is divisible is a substance; a Cartesian chunk of matter is divisible; therefore, a Cartesian chunk of matter is not a substance.  This points to the first part of Leibniz's critique of the Cartesianism mentioned above: namely, that according to Leibniz, Cartesian matter fails to have the unity required of a genuine substance. Indeed, in the Correspondence with Arnauld, Leibniz considers the case of a human body deprived of a soul and says the body, or cadaver, would not be a substance at all but merely an aggregate of substances. Moreover, anything lacking a substantial form or soul is not a substance, that is, if a thing is not truly “animated”, then it is only a true phenomenon. (G II 77/AG 80) It should be noted how strong Leibniz's claim is: he is arguing that Cartesian corporeal substances or any such chunks of matter are not real beings – at least not as real as simple substances.  Aggregates of simple substances, therefore, have a different ontological status from simple substances.