All our knowledge begins with the senses, proceeds then to the understanding, and ends with reason. There is nothing higher than reason.

The instruction of children should aim gradually to combine knowing and doing. Among all sciences mathematics seems to be the only one of a kind to satisfy this aim most completely.

It is precisely in knowing its limits that philosophy consists.

The only objects of practical reason are therefore those of good and evil. For by the former is meant an object necessarily desired according to a principle of reason; by the latter one necessarily shunned, also according to a principle of reason.

Man's greatest concern is to know how he shall properly fill his place in the universe and correctly understand what he must be in order to be a man.

This can never become popular, and, indeed, has no occasion to be so; for fine-spun arguments in favour of useful truths make just as little impression on the public mind as the equally subtle objections brought against these truths. On the other hand, since both inevitably force themselves on every man who rises to the height of speculation, it becomes the manifest duty of the schools to enter upon a thorough investigation of the rights of speculative reason, and thus to prevent the scandal which metaphysical controversies are sure, sooner or later, to cause even to the masses.

The desire which a man has for a woman is not directed towards her because she is a human being, but because she is a woman ; that she is a human being is of no concern to the man; only her sex is the object of his desires.