By providing for a National Legislature of two Houses, the Framers, deliberately or adventitiously, served several functions. Examples of both unicameralism and bicameralism abounded. Some of the ancient republics, to which the Framers often repaired for the learning of experience, had two-house legislatures, and the Parliament of Great Britain was based in two social orders, the hereditary aristocracy represented in the House of Lords and the freeholders of the land represented in the House of Commons. A number of state legislatures, following the Revolution, were created unicameral, and the Continental Congress, limited in power as it was, consisted of one house.
From the beginning in the Convention, in the Virginia Plan, a two-house Congress was called for. The Great Compromise, one of the critical decisions leading to a successful completion of the Convention, resolved the dispute about the national legislature by providing for a House of Representatives apportioned on population and a Senate in which the States were equally represented. The first function served, thusly, was federalism. 32 Coextensively important, however, was the separation-of-powers principle served. The legislative power, the Framers both knew and feared, was predominant in a society dependent upon the suffrage of the people, and it was important to have a precaution against the triumph of transient majorities. Hence, the Constitution's requirement that before lawmaking could be carried out bills must be deliberated in two Houses, their Members beholden to different constituencies, was in pursuit of this observation from experience. 33
Events since 1787, of course, have altered both the separation- of-powers and the federalism bases of bicameralism, in particular the adoption of the Seventeenth Amendment resulting in the popular election of Senators, so that the differences between the two Chambers are today less pronounced.
[Footnote 32] The Federalist, No. 39 (J. Cooke ed. 1961), 250-257 (Madison).
[Footnote 33] Id., No. 51, 347-353 (Madison). The assurance of the safeguard is built into the presentment clause. Article I, Sec. 7, cl. 2; and see id., cl. 3. The structure is not often the subject of case law, but it was a foundational matter in INS v. Chadha, 462 U.S. 919, 944 -951 (1983).