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

When I could have used a wife, I could not support one; and when I could support one, I no longer needed any

One who makes himself a worm cannot complain afterwards if people step on him.

There can be no doubt that all our knowledge begins with experience.

Both love of mankind, and respect for their rights are duties; the former however is only a conditional, the latter an unconditional, purely imperative duty, which he must be perfectly certain not to have transgressed who would give himself up to the secret emotions arising from benevolence.

At some future day it will be proved, I cannot say when and where, that the human soul is, while in earth life, already in an uninterrupted communication with those living in another world.

[A ruler is merely] the trustee of the rights of other men and he must always stand in dread of having in some way violated these rights.