The great end of life is not knowledge but action.

Every living creature commences its existence under a form different from, and simpler than, that which it eventually attains.

I am not afraid of the priests in the long-run. Scientific method is the white ant which will slowly but surely destroy their fortifications. And the importance of scientific method in modern practical life--always growing and increasing--is the guarantee for the gradual emancipation of the ignorant upper and lower classes, the former of whom especially are the strength of the priests.

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

The method of scientific investigation is nothing but the expression of the necessary mode of working of the human mind.

A man has no reason to be ashamed of having an ape for his grandfather. If there were an ancestor whom I should feel shame in recalling it would rather be a man who plunges into scientific questions with which he has no real acquaintance, only to obscure them by an aimless rhetoric.

Life is like walking along a crowded street--there always seem to be fewer obstacles to getting along on the opposite pavement--and yet, if one crosses over, matters are rarely mended.