Normal science, the activity in which most scientists inevitably spend most all their time, is predicated on the assumption that the scientific community knows what the world is like. Normal science often suppresses fundamental novelties because they are necessarily subversive of its basic commitments.

Rather than being an interpreter, the scientist who embraces a new paradigm is like the man wearing inverting lenses.

Far from being magisterial in its objectivity, science was conditioned by history, society, and the prejudices of scientists.

In science novelty emerges only with difficulty, manifested by resistance, against a background provided by expectation.

Normal science does not aim at novelties of fact or theory and, when successful, finds none.

Its assimilation requires the reconstruction of prior theory and re-evaluation of prior fact, an intrinsically revolutionary process that is seldom completed a single man and never overnight

Later scientific theories are better than earlier ones for solving puzzles in the often quite different environments to which they are applied. That is not a relativist's position, and it displays the sense in which I am a convinced believer in scientific progress.