 David Hume puts forward three main objections to the type of cosmological argument offered by Leibniz and Clarke (Hume 1779, Part IX, and the entry  Hume on religion).  The first is that the notion of (absolutely) necessary existence itself is problematic. Suppose that some being is absolutely necessary—then its nonexistence should be absolutely inconceivable. But, says Hume, for any being whose existence we can conceive, we can also conceive its nonexistence, and thus it isn’t a necessary being. Hume anticipates the objection that if we truly understood the divine nature, we would be unable to conceive God’s nonexistence. He replies that an analogous point can be made about matter: for all we know, if we truly understood the nature of matter, we would be unable to conceive its nonexistence. This would show that the existence of matter is not contingent after all, and that it does not require an external explanation. Thus, by parity, the cosmological argument does not establish that God is the necessary being who is responsible for the rest of the cosmos.