“If, therefore, from the settlement of the Saxons, to the introduction of Christianity among them, that system of religion could not be a part of the common law, because they were not yet Christians; and if, having their laws from that period to the close of the common law, we are able to find among them no such act of adoption; we may safely affirm (though contradicted by all the judges and writers on earth) that Christianity neither is, nor ever was, a part of the common law.['Whether Christianity is Part of the Common Law?', letter to Dr. Thomas Cooper, from Monticello, February 10, 1814]”

“I have observed, indeed, generally, that while in protestant countries the defections from the Platonic Christianity of the priests is to Deism, in catholic countries they are to Atheism. Diderot, D'Alembert, D’Holbach, Condorcet, are known to have been among the most virtuous of men. Their virtue, then, must have had some other foundation than the love of God.[Letter to Thomas Law, 13 June 1814]”

“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]”

“A strict observance of the written laws is doubtless one of the highest virtues of a good citizen, but it is not the highest. The laws of necessity, of self-preservation, of saving our country when in danger, are of higher obligation. To lose our country by a scrupulous adherence to written law would be to lose the law itself, with life, liberty, property and all those who are enjoying them with us; thus absurdly sacrificing the end to the means.”

“[Christianity is] the most ... perverted system that ever shone on man.”

“4. Religion. Your reason is now mature enough to examine this object. In the first place, divest yourself of all bias in favor of novelty & singularity of opinion... shake off all the fears & servile prejudices, under which weak minds are servilely crouched. 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 of the homage of reason, than that of blindfolded fear. You will naturally examine first, the religion of your own country. Read the Bible, then as you would read Livy or Tacitus. The facts which are within the ordinary course of nature, you will believe on the authority of the writer, as you do those of the same kind in Livy and Tacitus. The testimony of the writer weighs in their favor, in one scale, and their not being against the laws of nature, does not weigh against them. But those facts in the Bible which contradict the laws of nature, must be examined with more care, and under a variety of faces. Here you must recur to the pretensions of the writer to inspiration from God. Examine upon what evidence his pretensions are founded, and whether that evidence is so strong, as that its falsehood would be more improbable than a change in the laws of nature, in the case he relates. For example in the book of Joshua we are told the sun stood still several hours. Were we to read that fact in Livy or Tacitus we should class it with their showers of blood, speaking of statues, beasts, &c. But it is said that the writer of that book was inspired. Examine therefore candidly what evidence there is of his having been inspired. The pretension is entitled to your inquiry, because millions believe it. On the other hand you are astronomer enough to know how contrary it is to the law of nature that a body revolving on its axis as the earth does, should have stopped, should not by that sudden stoppage have prostrated animals, trees, buildings, and should after a certain time have resumed its revolution, & that without a second general prostration. Is this arrest of the earth's motion, or the evidence which affirms it, most within the law of probabilities? You will next read the New Testament. It is the history of a personage called Jesus. Keep in your eye the opposite pretensions: 1, of those who say he was begotten by God, born of a virgin, suspended & reversed the laws of nature at will, & ascended bodily into heaven; and 2, of those who say he was a man of illegitimate birth, of a benevolent heart, enthusiastic mind, who set out without pretensions to divinity, ended in believing them, and was punished capitally for sedition, by being gibbeted, according to the Roman law, which punished the first commission of that offence by whipping, & the second by exile, or death in fureâ....Do not be frightened from this inquiry by any fear of its consequences. If it ends in a belief that there is no God, you will find incitements to virtue in the comfort and pleasantness you feel in its exercise, and the love of others which it will procure you... In fine, I repeat, you must lay aside all prejudice on both sides, and neither believe nor reject anything, because any other persons, or description of persons, have rejected or believed it... I forgot to observe, when speaking of the New Testament, that you should read all the histories of Christ, as well of those whom a council of ecclesiastics have decided for us, to be Pseudo-evangelists, as those they named Evangelists. Because these Pseudo-evangelists pretended to inspiration, as much as the others, and you are to judge their pretensions by your own reason, and not by the reason of those ecclesiastics. Most of these are lost...[Letter to his nephew, Peter Carr, advising him in matters of religion, 1787]”

“We took the liberty to make some enquiries concerning the ground of their pretensions to make war upon nations who had done them no injury, and observed that we considered all mankind as our friends who had done us no wrong, nor had given us any provocation.The Ambassador [of Tripoli] answered us that it was founded on the Laws of their Prophet, that it was written in their Koran, that all nations who should not have acknowledged their authority were sinners, that it was their right and duty to make war upon them wherever they could be found, and to make slaves of all they could take as Prisoners, and that every Musselman who should be slain in battle was sure to go to Paradise.{Letter from the commissioners, John Adams & Thomas Jefferson, to John Jay, 28 March 1786}”