Reason should investigate its own parameters before declaring its omniscience.

In man (as the only rational creature on earth) those natural capacities which are directed to the use of his reason are to be fully developed only in the race, not in the individual.

Rules for Happiness: something to do, someone to love, something to hope for.

By a lie, a man... annihilates his dignity as a man.

Reason must approach nature with the view, indeed, of receiving information from it, not, however, in the character of a pupil, who listens to all that his master chooses to tell him, but in that of a judge, who compels the witnesses to reply to those questions which he himself thinks fit to propose. To this single idea must the revolution be ascribed, by which, after groping in the dark for so many centuries, natural science was at length conducted into the path of certain progress.

Freedom can never be comprehended, nor even can insight into it be gained.

Sincerity is the indispensable ground of all conscientiousness, and by consequence of all heartfelt religion.