James Madison, Federalist, no. 43, 29623 Jan. 1788
That useful alterations will be suggested by experience, could not but be foreseen. It was requisite therefore that a mode for introducing them should be provided. The mode preferred by the Convention seems to be stamped with every mark of propriety. It guards equally against that extreme facility which would render the Constitution too mutable; and that extreme difficulty which might perpetuate its discovered faults. It moreover equally enables the general and the state governments to originate the amendment of errors as they may be pointed out by the experience on one side or on the other. The exception in favour of the equality of suffrage in the Senate was probably meant as a palladium to the residuary sovereignty of the States, implied and secured by that principle of representation in one branch of the Legislature; and was probably insisted on by the States particularly attached to that equality. The other exception must have been admitted on the same considerations which produced the privilege defended by it.
The Founders' Constitution
Volume 4, Article 5, Document 6
The University of Chicago Press
Hamilton, Alexander; Madison, James; and Jay, John. The Federalist. Edited by Jacob E. Cooke. Middletown,
Easy to print version.