“Statesmen, my dear Sir, may plan and speculate for Liberty, but it is Religion and Morality alone, which can establish the Principles upon which Freedom can securely stand.”
Letter http://memory.loc.gov/cgi-bin/query/r?ammem/hlaw:@field(DOCID+@lit(dg004210)) to Zabdiel Adams (21 June 1776)
1770s
Context: Statesmen, my dear Sir, may plan and speculate for Liberty, but it is Religion and Morality alone, which can establish the Principles upon which Freedom can securely stand. The only foundation of a free Constitution is pure Virtue, and if this cannot be inspired into our People in a greater Measure than they have it now, They may change their Rulers and the forms of Government, but they will not obtain a lasting Liberty. They will only exchange Tyrants and Tyrannies.
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John Adams 202
2nd President of the United States 1735–1826Related quotes

Dissent, Liggett Co. v. Lee, 288 U.S. 517 (1933), at 580.
Judicial opinions
Last Will and Testament (20 November 1798), as quoted in Patrick Henry : Life, Correspondences and Speeches (1891) by William Wirt Henry, Vol. H, p. 631.
This also often appears (incorrectly) as "I have now disposed of all my property to my family; there is one thing more I wish I could give them, and that is the Christian Religion. If they had that, and I had not given them one shilling, they would be rich; and if they had not that, and I had given them all the world, they would be poor." This version goes back at least to 1823, when it appeared in the 29 November 1823 issue of The Manchester Iris, a Weekly Literary and Scientific Miscellany, vol. II, p. 387. A complete transcription https://web.archive.org/web/20160320205247/http://www.redhill.org/last_will.htm of the will may be found at the Red Hill Patrick Henry Memorial website.
1790s, Last Will and Testament (1798)
Trial of Mary Ann Carlile (1821), 1 St. Tr. (N. S.) 1050.

From the private journal of Secretary of State Adams (1820)
Context: The discussion of this Missouri question has betrayed the secret of their souls. In the abstract they admit that slavery is an evil, they disclaim it, and cast it all upon the shoulder of…Great Britain. But when probed to the quick upon it, they show at the bottom of their souls pride and vainglory in their condition of masterdom. They look down upon the simplicity of a Yankee’s manners, because he has no habits of overbearing like theirs and cannot treat negroes like dogs. It is among the evils of slavery that it taints the very sources of moral principle. It establishes false estimates of virtue and vice: for what can be more false and heartless than this doctrine which makes the first and holiest rights of humanity to depend upon the color of the skin?

Letter to Sheikh El-Messiri, (28 August 1798); published in Correspondance Napoleon edited by Henri Plon (1861), Vol.4, No. 3148, p. 420

Letter to Charles-Jean-François Depont (November 1789), quoted in Alfred Cobban and Robert A. Smith (eds.), The Correspondence of Edmund Burke, Volume VI: July 1789–December 1791 (1967), p. 42
1780s
Source: The Wizard of Zao (1978), Chapter 4 (p. 50)