The busier we are, the more acutely we feel that we live, the more conscious we are of life.

Even a man's exact imitation of the song of the nightingale displeases us when we discover that it is a mimicry, and not the nightingale.

Both love of mankind, and respect for their rights are duties; the former however is only a conditional, the latter an unconditional, purely imperative duty, which he must be perfectly certain not to have transgressed who would give himself up to the secret emotions arising from benevolence.

Every human being should always be treated as an end and never as a mere instrument.

There is nothing higher than reason.

Maturity is having the courage to use one's own intelligence!

Two things fill the mind with ever new and increasing admiration and awe, the oftener and more steadily we reflect on them: the starry heavens above me and the moral law within me.