No experimental result can ever kill a theory: any theory can be saved from counterinstances either by some auxiliary hypothesis or by a suitable reinterpretation of its terms.

There is no falsification before the emergence of a better theory.

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

Intellectual honesty consists in stating the precise conditions under which one will give up one's belief.

Indeed, this epistemological theory of the relation between theory and experiment differs sharply from the epistemological theory of naive falsificationism.

That sometimes clear ... and sometimes vague stuff ... which is ... mathematics.

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.