“There is not a truth existing which I fear, or would wish unknown to the whole world.”

“All should be laid open to you without reserve, for there is not a truth existing which I fear, or would wish unknown to the whole world.”

“I was bold in the pursuit of knowledge, never fearing to follow truth and reason to whatever results they led.”

“Some are whigs, liberals, democrats, call them what you please. Others are tories, serviles, aristocrats, &c. The latter fear the people, and wish to transfer all power to the higher classes of society; the former consider the people as the safest depository of power in the last resort; they cherish them therefore, and wish to leave in them all the powers to the exercise of which they are competent.”

“When we see religion split into so many thousand of sects, and I may say Christianity itself divided into its thousands also, who are disputing, anathematizing and where the laws permit burning and torturing one another for abstractions which no one of them understand, and which are indeed beyond the comprehension of the human mind, into which of the chambers of this Bedlam would a man wish to thrust himself.[Letter to George Logan, 12 November 1816]”

“It is incumbent on every generation to pay its own debts as it goes. A principle which if acted on would save one-half the wars of the world.”

“If by religion we are to understand sectarian dogmas, in which no two of them agree, then your exclamation on that hypothesis is just, "that this would be the best of worlds if there were no religion in it.”