I assert that, in any particular natural science, one encounters genuine scientific substance only to the extent that mathematics is present.

The schematicism by which our understanding deals with the phenomenal world ... is a skill so deeply hidden in the human soul that we shall hardly guess the secret trick that Nature here employs.

It is precisely in knowing its limits that philosophy consists.

Morality is not properly the doctrine of how we may make ourselves happy, but how we may make ourselves worthy of happiness.

Two things strike me dumb: the infinite starry heavens, and the sense of right and wrong in man.

What can I know? What ought I to do? What may I hope?

[Aristotle formal logic thus far (1787)] has not been able to advance a single step, and hence is to all appearances closed and completed.