 An a posteriori argument involves at least one premise whose justification essentially appeals to some sort of empirical fact or experience. The main demonstrative a posteriori argument is what Kant dubbed “the cosmological argument”. It is motivated by the familiar question “Why is there something rather than nothing?” and goes from the empirical fact of the existence of something (or of the cosmos as a whole, perhaps) to the existence of a first cause or ground of that cosmos that is, at least in part, not identical to that cosmos. Cosmological arguments are found across almost every philosophical tradition, and find prominence in the West in the writings of Aristotle, Avicenna, al-Gh&amp;amacr;z&amp;amacr;li, Maimonides, Aquinas, Locke, Leibniz, Samuel Clarke, and David Hume. Here we will start with Avicenna, but then focus largely on the early modern period.