If the hypothesis of evolution is true, living matter must have arisen from non-living matter; for by the hypothesis the condition of the globe was at one time such, that living matter could not have existed in it, life being entirely incompatible with the gaseous state.

The scientific imagination always restrains itself within the limits of probability.

It is the first duty of a hypothesis to be intelligible.

It is better to read a little and thoroughly than cram a crude undigested mass into my head, though it be great in quantity.

If there is anything in the world which I do firmly believe in, it is the universal validity of the law of causation.

To say that an idea is necessary is simply to affirm that we cannot conceive the contrary; and the fact that we cannot conceive the contrary of any belief may be a presumption, but is certainly no proof, of its truth.

Science is simply common sense at its best, that is, rigidly accurate in observation, and merciless to fallacy in logic.