When new turns of behavior cease to appear in the life of the individual, its behavior ceases to be intelligent.

The greatest mistake is to imagine that we never err.

Coining "Dismal Science" as a nickname for Political Economy

Habit and imitation--there is nothing more perennial in us than these two. They are the source of all working, and all apprenticeship, of all practice, and all learning, in this world.

Skepticism . . . is not intellectual only it is moral also, a chronic atrophy and disease of the whole soul.

Superstition! that horrid incubus which dwelt in darkness, shunning the light, with all its racks, and poison chalices, and foul sleeping draughts, is passing away without return. Religion cannot pass away. The burning of a little straw may hide the stars of the sky; but the stars are there and will reappear.

In every phenomenon the beginning remains always the most notable moment.