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

“I predict future happiness for Americans, if they can prevent the government from wasting the labors of the people under the pretense of taking care of them.” 

“I am certainly not an advocate for frequent and untried changes in laws and constitutions...but I know also that laws and constitutions must go hand in hand with the progress of the human mind.....”

“I [am] obliged to recur ultimately to my habitual anodyne, "I feel: therefore I exist." I feel bodies which are not myself: there are other existencies then. I call them "matter". I feel them changing place. This gives me "motion". Where there is an absence of matter, I call it "void", or "nothing", or "immaterial space". On the basis of sensation, of matter and motion, we may erect the fabric of all the certainties we can have or need.” 

“Do not bite at the bait of pleasure till you know there is no hook beneath it.”

“The fantastical idea of virtue and the public good being a sufficient security to the state against the commission of crimes...was never mine. It is only the sanguinary hue of our penal laws which I meant to object to. Punishments I know are necessary, and I would provide them strict and inflexible, but proportioned to the crime. Death might be inflicted for murder and perhaps for treason, [but I] would take out of the description of treason all crimes which are not such in their nature. Rape, buggery, etc., punish by castration. All other crimes by working on high roads, rivers, gallies, etc., a certain time proportioned to the offence... Laws thus proportionate and mild should never be dispensed with. Let mercy be the character of the lawgiver, but let the judge be a mere machine. The mercies of the law will be dispensed equally and impartially to every description of men; those of the judge or of the executive power will be the eccentric impulses of whimsical, capricious designing man.”

“Everything is useful which contributes to fix in the principles and practices of virtue.”

“A Man's management of his own purse speaks volumes about character”

“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.”

“I consider him [Alexander von Humboldt] the most important scientist whom I have met.”

“If once the people become inattentive to the public affairs, you and I, and Congress and Assemblies, Judges and Governors, shall all become wolves. It seems to be the law of our general nature, in spite of individual exceptions.” 

“A coward is much more exposed to quarrels than a man of spirit.”

“Good humor is one of the preservatives of our peace and tranquility” 

“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 would rather be exposed to the inconveniences attending too much liberty, than those attending too small a degree of it.”