30 Phil, Chapter 27, Hume, Touchstone 70: The Problem of Induction.

The logic behind induction is inherently circular, hence, the problem of induction. We expect future events to be like past events because this has generally been true in the past. This justification itself is inductive, making the whole process circular and self-referential. Although induction works effectively in predictable ways, the problem of induction remains a captivating puzzle without an easy solution.