Our civil rights have no dependance on our religious opinions, any more than our opinions in physics or geometry.

Thomas Jefferson, A Bill for Establishing Religious Freedom

I have been just reading the new constitution of Spain. One of its fundamental basis is expressed in these words: “The Roman Catholic religion, the only true one, is, and always will be, that of the Spanish nation. The government protects it by wise and just laws, and prohibits the exercise of any other whatever.” Now I wish this presented to those who question what you may sell, or we may buy, with a request to strike out the words, “Roman Catholic,” and to insert the denomination of their own religion. This would ascertain the code of dogmas which each wishes should domineer over the opinions of all others, and be taken, like the Spanish religion, under the “protection of wise and just laws.” It would shew to what they wish to reduce the liberty for which one generation has sacrificed life and happiness. It would present our boasted freedom of religion as a thing of theory only, and not of practice, as what would be a poor exchange for the theoretic thraldom, but practical freedom of Europe.

Thomas Jefferson, letter to N. G. Dufief, April 19, 1814

The generation which is going off the stage has deserved well of mankind for the struggles it has made, & for having arrested that course of despotism which had overwhelmed the world for thousands & thousands of years. If there seems to be danger that the ground they have gained will be lost again, that danger comes from the generation your cotemporary. But that the enthusiasm which characterises youth should lift its parricide hands against freedom & science, would be such a monstrous phenomenon as I cannot place among possible things in this age & this country.

Thomas Jefferson, letter to William Green Munford, June 18, 1799

Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus. If it could be understood it would not answer their purpose. Their security is in their faculty of shedding darkness, like the scuttle fish, thro’ the element in which they move, and making it impenetrable to the eye of a pursuing enemy. And there they will skulk, until some rational creed can occupy the void which the obliteration of their duperies would leave in the minds of our honest and unsuspecting brethren.

Thomas Jefferson, letter to Francis van der Kemp, August 6, 1816

They observe that on ignition of the needle or spring, Their magnetism and elasticity cease. So on dissolution of the material organ by death it’s action of thought may cease also. And that nobody supposes that the magnetism or elasticity retire to hold a substantive and distinct existence. These were the qualities only of particular conformations of matter: change the conformation, and it’s qualities change also. …… Were it necessary however to form an opinion, I confess I should, with Mr. Locke, prefer swallowing one incomprehensibility rather than two. It requires one effort only to admit the single incomprehensibility of matter endowed with thought: and two to believe, 1st. that of an existence called Spirit, of which we have neither evidence nor idea, and then 2dly. how that spirit which has neither extension nor solidity, can put material organs into motion. These are things which you and I may perhaps know ere long.

Thomas Jefferson, letter to John Adams, March 14, 1820

No man on earth has less taste or talent for criticism than myself, and least and last of all should I undertake to criticise works on the Apocalypse. It is between 50. and 60. years since I read it, and I then considered it as merely the ravings of a Maniac, no more worthy, nor capable of explanation than the incoherences of our own nightly dreams. …… There is not coherence enough in them to countenance any suite of rational ideas. You will judge therefore from this how impossible I think it that either your explanation, or that of any man in the heavens above, or on the earth beneath, can be a correct one. What has no meaning admits no explanation.

Thomas Jefferson, letter to Alexander Smyth, January 17, 1825

In every country and every age the priest has been hostile to liberty. He is always in alliance with the despot abetting his abuses in return for protection to his own. It is easier to acquire wealth and power by this combination than by deserving them: and to effect this they have perverted the purest religion ever preached to man, into mystery and jargon unintelligible to all mankind and therefore the safer engine for their purposes.

Thomas Jefferson, letter to Horatio Spafford, March 17, 1814

The most undesirable of all things is a long life and there is nothing I have ever dreaded so much. Altho’ subject to occasional indispositions my health is too good generally to give me fear on that subject. I am weak indeed in body, able scarcely to walk into my garden without too much fatigue, but a ride of 6, 8, or 10 miles a day gives me none. Still however a start or stumble of my horse or some one of the accidents which constantly beset us, may cut short the thread of life and relieve me from the evils of dotage. Come when it will it will find me neither unready nor unwilling.

Thomas Jefferson, letter to Benjamin Waterhouse, January 8, 1825

That form [of government] which we have substituted, restores the free right to the unbounded exercise of reason and freedom of opinion. All eyes are opened, or opening, to the rights of man. The general spread of the light of science has already laid open to every view the palpable truth, that the mass of mankind has not been born with saddles on their backs, nor a favored few booted and spurred, ready to ride them legitimately, by the grace of God. These are grounds of hope for others. For ourselves, let the annual return of this day [July 4] forever refresh our recollections of these rights, and an undiminished devotion to them.

Thomas Jefferson, letter (his last) to Roger Weightman, June 24, 1826

Jefferson had received an invitation to Fourth of July festivities in Washington, for the 50th anniversary of American independence. He was too old and ill, and declined. He died on July 4, 1826.

Calvinism has introduced into the Christian religion more new absurdities than it’s leader had purged it of old ones.

Thomas Jefferson, letter to Salma Hale, July 26, 1818

Yes, I saw the apostrophe. It’s original.