This paper aims to clarify the distinction between "natural" and "philosophical" relation on Hume's Treatise. Although there is scant textual evidence on this distinction, commentators have wrestled with this problem for more than half a century since the distinction is of great importance in making sense of Hume's two definitions of cause. Recently, Helen Beebee has offered a procedural interpretation, according to which, the distinction lies in the difference between processes we use in recognizing relation.
Although this procedural interpretation seems promising, it has something that needs clarification. Indeed, Peter Millican criticizes this interpretation. If this is understood in a particular way, it could be the case that we cannot advocate this procedural interpretation. What makes matters worse, Millican argues that there is no substantial distinction between natural and philosophical relation.
Thus, in this paper, I mainly wrestle with two issues concerning Beebee's interpretation. Firstly, I articulate her procedural interpretation, eliminating the ambiguity inherent in the word "process." Secondly, against Millican, I argue that the distinction between natural and philosophical is indeed a substantial distinction, playing a pivotal role in Hume's science of man.