It is an error to imagine that evolution signifies a constant tendency to increased perfection. That process undoubtedly involves a constant remodeling of the organism in adaptation to new conditions; but it depends on the nature of those conditions whether the direction of the modifications effected shall be upward or downward.

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

It is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty.

Living things have no inertia, and tend to no equilibrium.

If the twentieth century is to be better than the nineteenth, it will be because there are among us men who walk in Priestley's footsteps....To all eternity, the sum of truth and right will have been increased by their means; to all eternity, falsehoods and injustice will be the weaker because they have lived.

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

Deduction, which takes us from the general proposition to facts again-teaches us, if I may so say, to anticipate from the ticket what is inside the bundle.