In the mere concept of one thing it cannot be found any character of its existence.

This spirit of freedom is expanding even where it must struggle against the external obstacles of governments that misunderstand their own function. Such governments are illuminated by the example that the existence of freedom need not give cause for the least concern regarding public order and harmony in the commonwealth. If only they refrain from inventing artifices to keep themselves in it, men will gradually raise themselves from barbarism.

So act that anything you do may become universal law.

Metaphysics is a dark ocean without shores or lighthouse, strewn with many a philosophic wreck.

. . . as to moral feeling, this supposed special sense, the appeal to it is indeed superficial when those who cannot think believe that feeling will help them out, even in what concerns general laws: and besides, feelings which naturally differ infinitely in degree cannot furnish a uniform standard of good and evil, nor has any one a right to form judgments for others by his own feelings. . . .

The question is not so much whether there is life on Mars as whether it will continue to be possible to live on Earth

I am myself by inclination an investigator.