The members of the convention kept its secrets inviolate for many years.
With few exceptions, the great secrets of the convention died with them.
Only one, James Madison, left a comprehensive statement of the more
formal proceedings. With this notable exception, only a few anecdotes,
handed down by tradition, escaped oblivion. The first of the number to
break the pledge of secrecy was Robert Yates, Chief Justice of New York,
who, in 1821, published his recollections; but, as he had left the
convention a few months after it began, his notes ceased with the 5th of
July.

The world would thus have been for ever ignorant of the details of one
of the most remarkable conventions in the annals of mankind had it not
been that one of the ablest of their number, James Madison, regularly
attended the sessions and kept notes from day to day of the debates.
While he was not a stenographer, he had a gift for condensing a speech
and fairly representing its substance. He jealously guarded his Journal
of the Convention until his death. Its very existence was known to few.
He died in 1836, and four years later the government purchased the
manuscript from his widow. Then, for the first time, the curtain was
measurably raised upon the proceedings of a convention which had
created, as we now know, one of the greatest nations in history.
Fifty-three years after the close of the convention, and when nearly
every one of its participants were dead, Madison's Journal was first
published.

When was a great secret better kept? Grateful as posterity must be for
this inestimable gift of great human enterprise, yet even Madison's
careful journal fills one with the deepest regret that this wonderful
debate, which lasted for nearly four months between men of no ordinary
ability, could not have been preserved to the world.