Do what you can to do what you ought, and leave hoping and fearing alone.

Not far from the invention of fire we must rank the invention of doubt.

My reflection, when I first made myself master of the central idea of the 'Origin', was, 'How extremely stupid not to have thought of that!'

The sceptics end in the infidelity which asserts the problem to be insoluble, or in the atheism which denies the existence of any orderly progress and governance of things: the men of genius propound solutions which grow into systems of Theology or of Philosophy, or veiled in musical language which suggests more than it asserts, take the shape of the Poetry of an epoch.

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

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

It is one of the most saddening things in life that, try as we may, we can never be certain of making people happy, whereas we can almost always be certain of making them unhappy.