The more we come in contact with animals and observe their behaviour, the more we love them, for we see how great is their care of the young.

When a thoughtful human being has overcome incentives to vice and is aware of having done his bitter duty, he finds himself in a state that could be called happiness, a state of contentment and peace of mind in which virtue is its own reward.

Feminine traits are called weaknesses. People joke about them; fools ridicule them; but reasonable persons see very well that those traits are just the tools for the management of men, and for the use of men for female designs.

Intuition and concepts constitute... the elements of all our knowledge, so that neither concepts without an intuition in some way corresponding to them, nor intuition without concepts, can yield knowledge.

. . . 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. . . .

Always regard every man as an end in himself, and never use him merely as a means to your ends [i.e., respect that each person has a life and purpose that is their own; do not treat people as objects to be exploited].

Reason can never prove the existence of God.