David Hume (1711–1776) pushes empiricism until familiar assumptions start looking strange. We experience sequences of events, habits, feelings, and perceptions — but where exactly do ideas such as necessary causation, enduring selfhood, or rationally guaranteed induction come from?

Big idea: Repeated experience can train expectation without providing a non-circular logical proof that the future must resemble the past.

Consider causation. We observe one type of event repeatedly followed by another — Hume's constant conjunction — but we do not perceive an invisible necessary connection binding cause to effect. The felt necessity arises partly from the mind's learned expectation.

That leads to the problem of induction. Why should past regularities justify future predictions? Saying “because induction has worked in the past” uses induction to justify induction.

Hume does not conclude that we should stop predicting tomorrow or abandon science. Humans cannot avoid forming expectations from experience. His point is that this indispensable practice is not founded on the kind of deductive rational certainty philosophers often wanted.

Hume is also important for ethics and psychology: reason alone does not generate motivation, and moral judgment is deeply connected to sentiment.

Kant later said Hume awoke him from his “dogmatic slumber,” especially around causation — a useful intellectual bridge, though Kant's answer is not simply “Hume was wrong.”