Only the descent into the hell of self-knowledge can pave the way to godliness.

Apart from moral conduct, all that man thinks himself able to do in order to become acceptable to God is mere superstition and religious folly.

But only he who, himself enlightened, is not afraid of shadows.

Experience without theory is blind, but theory without experience is mere intellectual play.

Philosophy stands in need of a science which shall determine the possibility, principles, and extent of human knowledge à priori.

Enthusiasm is always connected with the senses, whatever be the object that excites it. The true strength of virtue is serenity of mind, combined with a deliberate and steadfast determination to execute her laws. That is the healthful condition of the moral life; on the other hand, enthusiasm, even when excited by representations of goodness, is a brilliant but feverish glow which leaves only exhaustion and languor behind.

The arts of speech are rhetoric and poetry. Rhetoric is the art of transacting a serious business of the understanding as if it were a free play of the imagination; poetry that of conducting a free play of the imagination as if it were a serious business of the understanding.