“The attempt of Lavoisier to reform chemical nomenclature is premature. One single experiment may destroy the whole filiation of his terms; and his string of sulphates, sulphites, and sulphures, may have served no end than to have retarded the progress of science by a jargon, from the confusion of which time will be requisite to extricate us.” 

“Difference of opinion is advantageous in religion. The several sects perform the office of a Censor morum over each other. Is uniformity attainable? Millions of innocent men, women, and children, since the introduction of Christianity, have been burnt, tortured, fined, imprisoned; yet we have not advanced one inch towards uniformity. What has been the effect of coercion? To make one half the world fools, and the other half hypocrites. To support roguery and error all over the earth. Let us reflect that it is inhabited by a thousand millions of people. That these profess probably a thousand different systems of religion. That ours is but one of that thousand. That if there be but one right, and ours that one, we should wish to see the 999 wandering sects gathered into the fold of truth. But against such a majority we cannot effect this by force. Reason and persuasion are the only practicable instruments. To make way for these, free enquiry must be indulged; and how can we wish others to indulge it while we refuse it ourselves.”

“. . . The spirit of resistance to government is so valuable on certain occasions, that I wish it to be always kept alive. It will often be exercised when wrong, but better so than not to be exercised at all. I like a little rebellion now and then. It is like a storm in the atmosphere.”

“Men have differed in opinion, and been divided into parties by these opinions, from the first origin of societies; and in all governments where they have been permitted freely to think and to speak. the same political parties which now agitate the U.S. have existed through all time. Whether the power of the people, or that of the (best men; nobles) should prevail, were questions which kept the states of Greece and rome in eternal convulsions...” 

“History, by apprising [the people] of the past, will enable them to judge of the future.” 

“To the corruptions of Christianity I am, indeed opposed; but not to the genuine precepts of Jesus himself. I am a Christian, in the only sense in which he wished any one to be; sincerely attached to his doctrines, in preference to all others.”

“The people cannot be all, and always, well informed. The part which is wrong will be discontented, in proportion to the importance of the facts they misconceive. If they remain quiet under such misconceptions, it is lethargy, the forerunner of death to the public liberty. ... What country before ever existed a century and half without a rebellion? And what country can preserve its liberties if their rulers are not warned from time to time that their people preserve the spirit of resistance? Let them take arms. The remedy is to set them right as to facts, pardon and pacify them. What signify a few lives lost in a century or two? The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants. It is its natural manure.”

“All tyranny needs to gain a foothold is for people of good conscience to remain silent.”

“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.”

“Politics, like religion, hold up the torches of martyrdom to the reformers of error.”

“Bigotry is the disease of ignorance, of morbid minds; enthusiasm of the free and buoyant. Education and free discussion are the antidotes of both. We are destined to be a barrier against the returns of ignorance and barbarism. Old Europe will have to lean on our shoulders, and to hobble along by our side, under the monkish trammels of priests and kings, as she can. What a Colossus shall we be when the Southern continent comes up to our mark! What a stand will it secure as a ralliance for the reason & freedom of the globe! I like the dreams of the future better than the history of the past. So good night. I will dream on, always fancying that Mrs Adams and yourself are by my side marking the progress and the obliquities of ages and countries.”

“I never considered a difference of opinion in politics, in religion, in philosophy, as cause for withdrawing from a friend.” 

“When describing the University of Virginia: Here, We are not afraid to follow truth wherever it may lead, nor to tolerate any error so long as reason is left free to combat it.”

“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]” 

“I am conscious that an equal division of property is impracticable. But the consequences of this enormous inequality [in Europe] producing so much misery to the bulk of mankind, legislators cannot invent too many devices for subdividing property,...[One] means of silently lessening the inequality of property is to exempt all from taxation below a certain point, and to tax the higher portions of property in geometrical progression as they rise.”