To be is to be perceived (Esse est percipi)." Or, "If a tree falls in the forest and no one is there to hear it, does it make a sound?

Did men but consider that the sun, moon, and stars, and every other object of the senses, are only so many sensations in their minds, which have no other existence but barely being perceived, doubtless they would never fall down and worship their own ideas; but rather address their homage to that eternal invisible Mind which produces and sustains all things.

Of all men living [priests] are our greatest enemies. If it were possible, they would extinguish the very light of nature, turn the world into a dungeon, and keep mankind for ever in chains and darkness.

A mind at liberty to reflect on its own observations, if it produce nothing useful to the world, seldom fails of entertainment to itself.

Certainly he who can digest a second or third fluxion need not, methinks, be squeamish about any point in divinity.

That neither our thoughts, nor passions, nor ideas formed by the imagination, exist without the mind, is what every body will allow.

That the discovery of this great truth, which lies so near and obvious to the mind, should be attained to by the reason of so veryfew, is a sad instance of the stupidity and inattention of men, who, though they are surrounded with such clear manifestations of the Deity, are yet so little affected by them, that they seem as it were blinded with excess of light.