“Whenever you do a thing, act as if all the world were watching.”

“I have examined all the known superstitions of the world,and I do not find in our particular superstition of Christianity one redeeming feature. They are all alike founded on fables and mythology. Millions of innocent men women and children since the introduction of Christianity,have been burnt, tortured, fined and imprisoned. What has been the effect of this coercion? To make one half the world fools and the other half hypocrites; to support roguery and error all over the earth.”

“Nothing can stop the man with the right mental attitude from achieving his goal; nothing on earth can help the man with the wrong mental attitude.”

“If it is believed that these elementary schools will be better managed by the governor and council or any other general authority of the government, than by the parents within each ward, it is a belief against all experience.”

“When the clergy addressed General Washington on his departure from the government, it was observed in their consultation that he had never on any occasion said a word to the public which showed a belief in the Christian religion and they thought they should so pen their address as to force him at length to declare publicly whether he was a Christian or not. They did so. However [Dr. Rush] observed the old fox was too cunning for them. He answered every article of their address particularly except that, which he passed over without notice... I know that Gouverneur Morris, who pretended to be in his secrets & believed himself to be so, has often told me that General Washington believed no more of that system than he himself did.

“An injured friend is the bitterest of foes.”

“A strong body makes the mind strong. As to the species of exercises, I advise the gun. While this gives moderate exercise to the body, it gives boldness, enterprise and independence to the mind. Games played with the ball and others of that nature are too violent for the body and stamp no character on the mind. Let your gun therefore be your constant companion of your walks.”

“Honesty is the first chapter in the book of wisdom.” 

“...We are all Federalists,and we are all Republicans.”

“To your request of my opinion of the manner in which a newspaper should be conducted, so as to be most useful, I should answer, ‘by restraining it to true facts & sound principles only.’ Yet I fear such a paper would find few subscribers. It is a melancholy truth, that a suppression of the press could not more compleatly deprive the nation of its benefits, than is done by its abandoned prostitution to falsehood. Nothing can now be believed which is seen in a newspaper. Truth itself becomes suspicious by being put into that polluted vehicle. The real extent of this state of misinformation is known only to those who are in situations to confront facts within their knolege with the lies of the day. I really look with commiseration over the great body of my fellow citizens, who, reading newspapers, live & die in the belief, that they have known something of what has been passing in the world in their time; whereas the accounts they have read in newspapers are just as true a history of any other period of the world as of the present, except that the real names of the day are affixed to their fables. General facts may indeed be collected from them, such as that Europe is now at war, that Bonaparte has been a successful warrior, that he has subjected a great portion of Europe to his will, &c., &c.; but no details can be relied on. I will add, that the man who never looks into a newspaper is better informed than he who reads them; inasmuch as he who knows nothing is nearer to truth than he whose mind is filled with falsehoods & errors. He who reads nothing will still learn the great facts, and the details are all false.” —Letter to John Norvell, 14 June 1807 [Works 10:417--18]” 

“Later, he told his nephew that religion required careful thought, not reflexive acceptance. "Fix reason firmly in her seat, and call to her tribunal every fact, every opinion. Question with boldness even the existence of a God; because, if there be one, he must more approve the homage of reason, than that of blindfolded fear”

“I am bold to Say that neither you nor I, will live to See the Course which 'the Wonders of the Times' will take. Many Years, and perhaps Centuries must pass, before the current will acquire a Settled direction... yet Platonic, Pythagoric, Hindoo, and cabalistic Christianity, which is Catholic Christianity, and which has prevailed for 1,500 years, has received a mortal wound, of which the monster must finally die. Yet so strong is his constitution, that he may endure for centuries before he expires.

“That ideas should freely spread from one to another over the globe, for the moral and mutual instruction of man, and improvement of his condition, seems to have been peculiarly and benevolently designed by nature, when she made them, like fire, expansible over all space, without lessening their density in any point, and like the air in which we breathe, move, and have our physical being, incapable of confinement or exclusive appropriation. Inventions then cannot, in nature, be a subject of property.”

“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.” 

“Even in Europe a change has sensibly taken place in the mind of man. Science has liberated the ideas of those who read and reflect, and the American example has kindled feelings of right in the people.”