An experiment not worth doing is not worth doing well.

Deductivism in mathematical literature and inductivism in scientific papers are simply the postures we choose to be seen in when the curtain goes up and the public sees us. The theatrical illusion is shattered if we ask what goes on behind the scenes. In real life discovery and justification are almost always different processes.

It is ... a sign of the times-though our brothers of physics and chemistry may smile to hear me say so-that biology is now a science in which theories can be devised: theories which lead to predictions and predictions which sometimes turn out to be correct. These facts confirm me in a belief I hold most passionately-that biology is the heir of all the sciences.

Scientific reasoning is a dialogue between the possible and the actual, between proposal and disposal between what might be true, and what is in fact the case.

The Phenomenon of Man stands square in the tradition of Naturphilosophie, a philosophical indoor pastime of German origin which does not seem even by accident (though there is a great deal of it) to have contributed anything of permanent value to the storehouse of human thought.

All scientists know of colleagues whose minds are so well equipped with the means of refutation that no new idea has the temerity to seek admittance. Their contribution to science is accordingly very small.

The alternative to thinking in evolutionary terms is not to think at all.