“The hocus-pocus phantasm of a God like another Cerberus, with one body and three heads, had its birth and growth in the blood of thousands and thousands of martyrs... In fact, the Athanasian paradox that one is three, and three but one, is so incomprehensible to the human mind, that no candid man can say he has any idea of it, and how can he believe what presents no idea? He who thinks he does, only deceives himself. He proves, also, that man, once surrendering his reason, has no remaining guard against absurdities the most monstrous, and like a ship without a rudder, is the sport of every wind. With such persons, gullibility which they call faith, takes the helm from the hand of reason, and the mind becomes a wreck.

“Whenever any form of government becomes destructive of these ends [life, liberty, and the pursuit of happiness] it is the right of the people to alter or abolish it, and to institute new government...” 

“What a stupendous, what an incomprehensible machine is man! Who can endure toil, famine, stripes, imprisonment and death itself in vindication of his own liberty, and the next moment . . . inflict on his fellow men a bondage, one hour of which is fraught with more misery than ages of that which he rose in rebellion to oppose.”

“He who knows best knows how little he knows.”

“There is a ripeness of time for death,  regarding others as well as ourselves, when it is reasonable we should drop off, and make room for  another growth. When we have lived our generation out, we should not wish to encroach on another.”

“I have sworn upon the altar of god, eternal hostility against every form of tyranny over the mind of man.”

“A little patience, and we shall see the reign of witches pass over, their spells dissolve, and the people, recovering their true sight, restore their government to its true principles. It is true that in the meantime we are suffering deeply in spirit, and incurring the horrors of a war and long oppressions of enormous public debt...If the game runs sometime against us at home, we must have patience till luck turns, and then we shall have an opportunity of winning back the principles we have lost, for this is a game where principles are at stake.” 

“Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong.”

“The art of life is the art of avoiding pain; and he is the best pilot, who steers clearest of the rocks and shoals with which it is beset.”

“Nothing was or is farther from my intentions, than to enlist myself as the champion of a fixed opinion, where I have only expressed doubt.”

“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]” 

“If there is one principle more deeply rooted in the mind of every American, it is that we should have nothing to do with conquest.”

“In matters of principal stand like a rock.”

“I know no safe depository of the ultimate powers of the society but the people themselves ; and if we think them not enlightened enough to exercise their control with a wholesome discretion, the remedy is not to take it from them, but to inform their discretion by education. This is the true corrective of abuses of constitutional power.” 

“You seem to consider the judges as the ultimate arbiters of all constitutional questions; a very dangerous doctrine indeed, and one which would place us under the despotism of an oligarchy. Our judges are as honest as other men, and not more so. They have, with others, the same passions for party, for power, and the privilege of their corps.... Their power [is] the more dangerous as they are in office for life, and not responsible, as the other functionaries are, to the elective control. The Constitution has erected no such single tribunal, knowing that to whatever hands confided, with the corruptions of time and party, its members would become despots. It has more wisely made all the departments co-equal and co-sovereign within themselves.”