 According to Leibniz, bodies (qua material) are aggregates, and an aggregate, of course, is not a substance on account of its lack of unity. The claim in the above passage is that whatever being or reality an aggregate has derives from the being and reality of its constituents. Thus, Leibniz thinks that if a body is to have any reality at all, if it is to be more than a mere “phenomenon, lacking all reality as would a coherent dream,” then it must ultimately be composed of things which are real beings. Atoms, he claims, are unfit for this role, because they are themselves extended beings, and for Leibniz, divisibility is of the essence of extension. That is, those who believe in indivisible atoms make matter “divisible in one place, indivisible in another” (On Nature Itself (1698); G IV, 513/A&amp;G 165), but “we cannot explain why bodies of a definite smallness [i.e. atoms] should not be further divisible” (Primary Truths (1686); C 522/A&amp;G 34). Every extended mass, for Leibniz, is composed of extended parts, and so even if we could conceive of an atom as composed of parts which cannot be physically divided, “an invincible attachment of one part to another would not at all destroy the diversity of these parts” (New System of Nature, (1695); G IV, 482/W&amp;F 16), or it would not at all overcome the fact that it is an aggregate composed of parts and not truly one being. Likewise, mathematical points, “even an infinity of points gathered into one, will not make extension,” (to Des Bosses, 30 April 1709; G II, 370/L 597) and so cannot be understood as the constituents of extended bodies. Hence, Leibniz opts for the last of the above quoted alternatives: the constituents of bodies are “certain substances … that possess a true unity.” These substances are partless, unextended, and indivisible, and therefore real beings in Leibniz’s sense. Indeed, in several writings, Leibniz invites us to conceive of these substances on the model of our notion of souls. These simple substances are the only things which suffice for grounding the reality of bodies. To be sure, substances, Leibniz tells us, do not constitute a body as parts of the body, but as the “first elements,” or “primitive unities,” of the body. As he sometimes puts it, bodies “result from” these constitutive unities. That is, bodies just are aggregates of substances which appear to us as extended corporeal phenomena, though they are “well-founded” phenomena; they have their foundation in real beings.