 Clarke tells us that his argument for the being and attributes of God was done “partly by metaphysical Reasoning, and partly from the Discoveries (principally those that have been lately made) in Natural Philosophy” (W 2.581). His argument, which was known in Clarke’s time as “the argument a priori,” occupies most of A Demonstration of the Being and Attributes of God, Clarke’s first set of Boyle Lectures. (Note that Clarke’s use of the term “a priori” is not that which has been standard since Kant. The argument is a priori not primarily because it is available independent of experience, but because it argues from the nature of the cause to the nature of the effect; this is in contrast with the argument a posteriori which works from the effects — e.g., the design of the world— to the cause — e.g., the designer.) The argument is typically classified today as cosmological, but it should not be confused with the kalam cosmological argument (which takes as a premise that the world has a finite history). Clarke’s version belongs to the tradition of modal cosmological arguments that employ the principle of sufficient reason to argue from a contingent series of causes to a necessary being. The main lines of Clarke’s “argument a priori” are as  follows.[1]