Immediately after discussing what we identified in  Chap. 6 as transcendental causation in 1.4.2, Hume introduces his four-part system. A detailed explanation of this system is lacking in the literature, although Kemp Smith (1941), does parse it into respective parts, and gives a brief explanation of it as a four part system (pp. 474–487). However, in the next few chapters I give a much more exhaustive account.