What Can You Actually Know?
You believe the sun will rise tomorrow because it always has. But is that a good reason? Is there any rational basis for thinking the future will resemble the past?
David Hume identified the 'problem of induction' in the 1730s: we cannot justify our belief that patterns will continue without assuming that patterns continue, which is circular. Every empirical belief you hold rests on this unproven foundation. Science has not solved this; it has learned to live with it.
Hume, D. (1739). A Treatise of Human Nature. Printed for John Noon.
The problem
You've seen the sun rise every day of your life. You're confident it will rise tomorrow. What justifies that confidence?
The obvious answer: induction. The future has always resembled the past in this respect, so it will continue to do so.
But this argument is circular. You're using induction (the future resembles the past) to justify induction (so the future will resemble the past). You can't justify a principle of reasoning by using that very principle.
Hume's diagnosis
Hume concluded that our belief in the uniformity of nature is not rationally justified. It's a habit of mind, a natural disposition built by experience and necessary for survival. We can't help believing the sun will rise. But that's a psychological fact about us, not a logical justification.
This is unsettling because all of empirical science rests on induction. Every law of physics, every medical study, every engineering guarantee is an inductive claim: "this is how things have behaved, therefore this is how they'll behave."
Karl Popper's response
Popper argued we should stop trying to justify induction and instead focus on falsification. Science doesn't prove theories. It just hasn't yet disproven them. A good scientific theory is one that could be falsified but hasn't been yet. This shifts the game from verification to bold conjectures and severe tests.
It doesn't solve Hume's problem. It sidesteps it. But it gives science a workable methodology.
The practical question
Hume's problem lives in everyday life. You trust your car will start, assume your friends will behave as they have before, and bet your financial future on the stability of institutions. None of these are rationally guaranteed. They're inductive extrapolations from past experience.
What belief do you hold most firmly that, at its foundation, rests entirely on the fact that it's been true before?