Blind commitment to a theory is not an intellectual virtue: it is an intellectual crime.

The classical example of a successful research programme is Newton's gravitational theory: possibly the most successful research programme ever.

It would be wrong to assume that one must stay with a research programme until it has exhausted all its heuristic power, that one must not introduce a rival programme before everybody agrees that the point of degeneration has probably been reached.

Philosophy of science without history of science is empty; history of science without philosophy of science is blind.

Research programmes, besides their negative heuristic, are also characterized by their positive heuristic.

In degenerating programmes, however, theories are fabricated only in order to accommodate known facts

Mathematics does not grow through a monotonous increase of the number of indubitably established theorems but through the incessant improvement of guesses by speculation and criticism, by the logic of proofs and refutations.