David Hume argues that, "All inferences from experience...are effects of custom not of reasoning" (Enquiry, p. 28). This statement can be broken down into two parts: (1) all inductive inferences (inferences from experience) are not rationally justified and (2) all inductive inferences are effects of custom.
             To understand the first part of our study, we must understand what Hume means by "reasoning" (i.e. rationally justified). According to Hume, all objects of human reasoning are of two kinds, Relation of Ideas and Matters of Fact (p. 15). The truth of a proposition concerning the Relation of Ideas is discoverable by the pure operation of thought, independent of any existing object; such propositions are validated in that their negation involves or implies a contradiction (p. 15). For example: All black dogs are black; (negation) some black dogs are not black. One need not examine any black dog to ensure of its blackness; moreover, the negation of such a premise would imply a contradiction. Therefore, the proposition that all black dogs are black is justified by reason alone.
             The truth of statements concerning Matters of Fact is not achieved in the same way as the truth of statements concerning the Relation of Ideas. Statements of Matters of Fact are justified by experience, namely sense perception, memory, and cause-effect reasoning (p. 16). Unlike statements of Relation of Ideas, the negations of Statement of Matter of Fact do not imply any contradictions (p. 16). The following are examples of statements of Matters of Fact: this is a blue chair (depends on sense perception); it rained yesterday (depends on memory); the sun will rise tomorrow (depends on cause-effect reasoning)-again, the negation of any of these does not imply a contradiction in the statement.
             In his enquiry, Hume notices a difference between the justifications of sense perception and memory compared to cause-effect reasoning. With ...