 It was traditional enough to say that God (and only God) is being in the strictest sense, and is the cause of existence to all other beings. But Fârâbî’s version is importantly different. Fârâbî is taking up Aristotle’s program of defining each thing through its essential cause, and arguing that this kind of cause of X’s existing (such that something would not be an X if it were caused in some other way) is the existence [wujûd] of X and has a stronger claim to the title of being [mawjûd] than X: if this causal chain leads ultimately to God, so that God is ultimately involved in the quiddity of each other thing, then Fârâbî will have a scientific Aristotelian way of filling in the program of the Aims of the Metaphysics, of showing how an analysis of being and of its causes (once we grasp the relevant senses of being and of cause) will lead to God as the first cause of being and universal first principle. As this is presented in the Book of Letters, it is just a program for research, which might or might not lead up to a single first cause of existence from which all other beings can be derived carried out. But in the Perfect City and the Political Regime Fârâbî gives at least a sketch of the upward causal argument to God as a single first cause of existence, and of the downward path from God to all other beings. Fârâbî sees a charter for this causal investigation of the existence of thing especially in Aristotle’s Posterior Analytics II.