GOD Spinoza, on the other hand, was not at all a betting man: he liked his reasons as cut and dried as possible The existence of God, he believed, could be shown to be as plain to see as the truth of any proposition in Euclid To show this he presented his own version of the ontological argument, set out in geometrical form, in the Wrst book of his Ethics Proposition 11 of that book reads: ‘God, a substance consisting of inWnite attributes, each of which expresses an eternal and inWnite essence, necessarily exists.’ The description here given of God is derived from the sixth of the series of deWnitions set out at the beginning of the book The proof of proposition 11 is by reductio ad absurdum: If you deny this, conceive, if you can, that God does not exist Therefore (by Axiom 7) his essence does not involve existence But this (by Proposition 7) is absurd Therefore, God necessarily exists Q.E.D (Eth, 7) If we look up Axiom 7, we Wnd that it says that if a thing can be conceived as non-existing its essence does not involve existence Proposition is more controversial: existence is part of the nature of a substance To prove this, Spinoza tells us that a substance cannot be produced by anything else, and so must be its own cause; that is to say, its essence must involve existence But why cannot a substance be produced by something else—by another substance? We are referred to Proposition (there cannot be two or more substances with the same attribute) and to Proposition (if A is to be the cause of B, A must have something in common with B) These in turn rest on DeWnition 3, the initial deWnition of substance as ‘that which is in itself and is conceived by itself, so that its concept can be formed independently of the concept of any other thing’ (Eth, 1) Two elements in Spinoza’s argument are counterintuitive Are we not surrounded in life by cases of substances giving rise to other substances, most conspicuously living things generating other living things? And why should we accept the claim that if B is the cause of A, then the concept of B must be part of the concept of A? It is not possible to know what lung cancer is without knowing what a lung is, but is it not possible to know what lung cancer is without knowing what the cause of lung cancer is? Spinoza is identifying causal relationships and logical relationships in a manner that is surely unwarranted But it is not, of course, inadvertent: the equivalence of the two kinds of consequence, logical and causal, is a key element of his 310