As men's habits of mind differ, so that some more readily embrace one form of faith, some another, for what moves one to pray may move another to scoff, I conclude ... that everyone should be free to choose for himself the foundations of his creed, and that faith should be judged only by its fruits.

Whatsoever is contrary to nature is contrary to reason, and whatsoever is contrary to reason is absurd.

Men believe themselves to be free, simply because they are conscious of their actions, and unconscious of the causes whereby those actions are determined.

The endeavor to understand is the first and only basis of virtue.

I believe that a triangle, if it could speak, would say that God is eminently triangular, and a circle that the divine nature is eminently circular; and thus would every one ascribe his own attributes to God.

[Believers] are but triflers who, when they cannot explain a thing, run back to the will of God; this is, truly, a ridiculous way of expressing ignorance.

The order and connection of ideas is the same as the order and connection of things.