Science works. That is not seriously in dispute, and any philosophy of science that implies otherwise has gone wrong somewhere. The interesting problem is that when philosophers try to specify precisely why it works — what rule scientists follow that others do not — the tidy answers keep failing on close inspection.
Take the obvious proposal: science is what is confirmed by observation. Popper's objection is that confirmation is cheap. Astrology, conspiracy theories and pseudo-medicine all accumulate confirming instances happily, because a sufficiently flexible theory can absorb any observation. What distinguishes a scientific claim, he argued, is that it forbids something — it sticks its neck out and could be shown wrong.
RevolutionHow science actually changes.
Thomas Kuhn complicated the picture by looking at history rather than logic. Science, he argued, does not accumulate steadily. Most of the time researchers work within a paradigm — a shared framework of assumptions, methods, and exemplary problems — doing what he called normal science, which is essentially puzzle-solving within accepted rules. Anomalies accumulate, are set aside, and eventually reach a point where the framework itself gives way. The resulting shift is not merely a change of belief but a change in what counts as a question worth asking.
Kuhn's controversial claim was that competing paradigms can be incommensurable — lacking a fully neutral standard by which to compare them, since the standards themselves are part of what changes. Critics argued this makes theory choice irrational or merely sociological. Kuhn resisted that reading, holding that good reasons operate in such choices even where no algorithm settles them, which is arguably how most difficult judgement works.
RealismDoes science describe reality?
A final divide. Scientific realists hold that successful theories are approximately true and that their unobservable entities — electrons, fields, genes — really exist; the alternative, they argue, would make science's predictive success an inexplicable miracle. Anti-realists reply that the aim of science is empirical adequacy rather than truth, and point to the historical record: theories that were highly successful, such as the luminiferous ether, turned out to posit entities that do not exist. If past successful theories were wrong about what exists, present success is weaker evidence than it appears.
None of this undermines science, and it is worth saying so plainly, because these debates are sometimes misused for exactly that. That we cannot fully articulate why a method works is a problem for philosophy, not evidence against the method. Science remains the most reliable instrument we have for finding out about the world; philosophy of science is the attempt to understand the instrument, not to dull it.