With the US House of Representatives representing the people, and the US Senate representing the states (more so prior to the adoption of the 17^th Amendment, but that’s another discussion), the US Congress is a recognizable extension of the “mixed-government” rationale for legislative bicameralism. Known to the early Americans largely through its British example, each chamber represents a different interest. In the British case, the commoners had one house, the aristocrats the other. Because the British monarch also had to agree to any legislation, the framework insured that legislation adopted in Britain had the unanimous consent of the three British estates – commons, aristocracy, and monarchy. It was a unanimity-promoting device in its classic setting.

For the then-proposed US national Congress, as James Madison discusses in The Federalist #62, legislation would be adopted with “the concurrence, first, of a majority of the people, and then, of a majority of the States.” Although not a mixed regime, analogous to a mixed regime’s bicameral rationale, the different congressional houses would represent different interests at the national level in the United States.

Largely underappreciated, matters were different at the state level. The debate over state-level cameral choice during the founding period was also explicit and self-conscious. A common anachronism suggests that the states adopted bicameralism due to the national example. Perhaps it’s true later, but it can’t be true at the start. After all, the national congress under the Articles of Confederation was a unicameral body. State legislatures predate the Constitution of 1788 by ten years.

So, too, at the time, the British bicameral example, and the mixed-government theory upon which it was based, was more of a negative in the case for bicameralism than a positive. Joseph Story observed that the case for bicameralism early in the US had to overcome “all the prejudices against a second co-ordinate legislative assembly” that were “stimulated by the exemplification of it in the British parliament.” Indeed, Pennsylvania, Georgia, and then Vermont initially had unicameral legislatures. (Georgia didn’t go bicameral until 1789, Pennsylvania in 1790, and Vermont not until 1836.)

And contrary to popular perceptions, the state-level constitutionalists of the founding era were largely republican through and through, and so they were constitutionally committed to apportioning state legislatures, whether bicameral or not, on the basis of population. Historian Marc Kruman writes that “Americans of the founding era rejected the notion that the senate should represent property and the house, persons.” Kruman reports that most of the original state bicameral legislatures did not represent geographic units in their upper legislative chambers but were apportioned by population.

The state-level commitment to thorough-going republicanism, however, decimated the mixed-polity rationale for bicameralism: If everyone in a polity is a commoner, then a second legislative chamber serves no purpose.

Americans of the era explicitly recognized the inconsistency. Thomas Jefferson, for example, criticized the proposed Virginia state senate because “being chose by the same electors” as Virginia’s House of Delegates, it was “too homogenous with the House of Delegates.” This left no justification for a second chamber according to Jefferson. He argued that second legislative chambers were useless unless they “introduce the influence of different interests or different principles” relative to the first chamber.

Gordon S. Wood notes more generally that the early “homogeneity of [social] orders” in the US resulted in “two homogenous branches” in state bicameral legislatures. Wood concludes, “The people in the new states seemed to be electing the same kinds of persons to both houses of the legislatures, thus creating a homogeneity of interest between the two branches and destroying the purpose for instituting a mixed polity.”

Were second legislative chambers nothing more than vestigial institutions of the bygone era (for the US, at least) of a mixed polity?

Debate over state constitutions during the founding period led to bicameralism being re-grounded in an entirely different theory.

James Wilson led the charge against Pennsylvania’s unicameral legislature. In doing so, he re-grounded the justification for bicameralism. The justification no longer lay in representing different interests – that made no sense in a polity that was entirely republican. Rather, bicameralism promoted better deliberation and, therefore, better legislative outcomes. For Wilson, the benefit of bicameralism in republican polities flowed not from the class separation of legislators in the two chambers, but from the acoustic separation of legislators in the two chambers.

He argued,

[Many] reasons . . . may be assigned, why all the advantages, to be expected from two branches of a legislature, may be gained and preserved, though those two branches derive their authority from precisely the same source.  . . . [These include a] double source of information, precision, and sagacity in planning, digesting, composing, comparing, and finishing the laws, both in form and substance.

Indeed, in Wilson’s argument, constitutionalists should resist the temptation to induce different political interests across the two chambers; doing so only invites legislative failure and is contrary to republicanism. “The Council and Assembly would both draw their power from the same source – from the people, the fountain of all authority. They could not have opposite interests, which are the causes of frequent contests.”

Wilson’s position was not without its critics. As Wood writes, “The homogeneity of interests between the two houses  . . . promoted by Wilson was precisely the deficiency of the American mixed governments that men like Jefferson and Madison were worried about.”

But in this Wilson was ahead of his contemporaries. Instead of trying to shoehorn the mixed-government rationale for bicameralism into the novel American context, Wilson jettisoned the underlying assumption entirely, and reworked the theory from a thoroughly republican starting point. In this, the rationale for state-level bicameralism in the US not only stands apart from the classical, mixed-government rationale for bicameralism, but also stands apart from the rationale for bicameralism at the national level in the US as well.