Science is perhaps the only human activity in which errors are systematically criticized and, in time, corrected.

Do not allow your dreams of a beautiful world to lure you away from the claims of men who suffer here and now. Our fellow men have a claim to our help; no generation must be sacrificed for the sake of future generations.

There will be well-testable theories, hardly testable theories, and non-testable theories. Those which are non-testable are of no interest to empirical scientists. They may be described as metaphysical.

We hate the very idea that our own ideas may be mistaken, so we cling dogmatically to our conjectures.

Piecemeal social engineering resembles physical engineering in regarding the ends as beyond the province of technology.

While differing widely in the various little bits we know, in our infinite ignorance we are all equal.

To give a causal explanation of an event means to deduce a statement which describes it, using as premises of the deduction one or more universal laws, together with certain singular statements, the initial conditions ... We have thus two different kinds of statement, both of which are necessary ingredients of a complete causal explanation.