Hearn (1970) notes that what Hume calls ‘general rules’ should be distinguished into two types. The first one are the eight rules Hume mentions in Treatise 1.3.15 as normative; the second one are the mere natural inclinations of our imagination. Following Hearn, many scholars try to extract from the writings the distinguishable criterion of ‘good’ rules. On the contrary, I try to understand the common feature, or the origin, of apparently different types of general rules. My interpretation will offer a naturalistic explanation of epistemic normativity of Hume's general rules.