By "essence" I understand a universal, of any degree of complexity and definition, which may be given immediately, whether to sense or to thought.... This object of pure sense or pure thought, with no belief superadded, an object inwardly complete and individual, but without external relations or physical status, is what I call an essence.

A great man need not be virtuous, nor his opinions right, but he must have a firm mind, a distinctive luminous character.

Man alone knows that he must die; but that very knowledge raises him, in a sense, above mortality, by making him a sharer in the vision of eternal truth. He becomes the spectator of his own tragedy; he sympathizes so much with the fury of the storm that he has no ears left for the shipwrecked sailor, though the sailor were his own soul. The truth is cruel, but it can be loved, and it makes free those who have loved it.

Spirit itself is not human; it may spring up in any life... it may exist in all animals, and who know in how many undreamt-of beings, or in the midst of what worlds?

Eternal vigilance is the price of knowledge.

The aim of education is the condition of suspended judgment on everything.

People are usually more firmly convinced that their opinions are precious than that they are true.