It is precisely in knowing its limits that philosophy consists.

Human beings are never to be treated as a means but always as ends.

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.

Freedom in the practical sense is the independence of the power of choice from necessitation by impulses of sensibility

There is nothing higher than reason.

Act in such a way that you treat humanity, whether in your own person or in the person of any other, never merely as a means to an end, but always at the same time as an end.

The light dove, cleaving the air in her free flight, and feeling its resistance, might imagine that its flight would be still easier in empty space.