The sources as well as the form of Kant’s position are complex. Kant was deeply impressed by what he knew of Leibniz (many of the texts that are crucial to later understandings of Leibniz, such as “Primary Truths”, having been unknown in Kant’s times, or others, such as the New Essays on Human Understanding, having been published only when he was well into his career) and the view that space and time are phaenomena bene fundata as well as by what he knew of Hume and his view that causation is a