The Constitution of the United States was made not merely for the generation that then existed, but for posterity- unlimited, undefined, endless, perpetual posterity.
Meaning of the quote
The Constitution of the United States was not just made for the people living at that time, but for all future generations to come, forever and ever. The founders wanted the Constitution to last and be used by people for a very, very long time, even for generations that haven't been born yet.

About Henry Clay
Henry Clay Sr. was a renowned American lawyer and statesman who represented Kentucky in the U.S. Senate and House of Representatives. He served as the seventh House speaker and the ninth secretary of state, and was known as the “Great Compromiser” for his role in defusing sectional crises. Clay unsuccessfully ran for president three times but left a lasting impact on American politics.
More quotes from Henry Clay
I would rather be right than President.
American politician from Kentucky (1777-1852)
If you wish to avoid foreign collision, you had better abandon the ocean.
American politician from Kentucky (1777-1852)
I have heard something said about allegiance to the South. I know no South, no North, no East, no West, to which I owe any allegiance.
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I had rather be right than be President.
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Statistics are no substitute for judgment.
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Government is a trust, and the officers of the government are trustees. And both the trust and the trustees are created for the benefit of the people.
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Courtesies of a small and trivial character are the ones which strike deepest in the grateful and appreciating heart.
American politician from Kentucky (1777-1852)
An oppressed people are authorized whenever they can to rise and break their fetters.
American politician from Kentucky (1777-1852)
Of all human powers operating on the affairs of mankind, none is greater than that of competition.
American politician from Kentucky (1777-1852)
Of all the properties which belong to honorable men, not one is so highly prized as that of character.
American politician from Kentucky (1777-1852)
The Constitution of the United States was made not merely for the generation that then existed, but for posterity- unlimited, undefined, endless, perpetual posterity.
American politician from Kentucky (1777-1852)