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What Is a Bicameral Legislature, and Why Does the U.S. Have One?

A bicameral legislature is a legislative body made up of two (bi) chambers (camera). It is distinguished from a unicameral legislature in which all members of the legislature belong to and vote in one house. The United Kingdom's system of government includes a bicameral legislature, made up of the House of Commons and the House of Lords. Meanwhile, a typical city council in the U.S. is an example of a unicameral legislature.

In the United States, the U.S. House of Representatives acts as the “lower house,” while the U.S. Senate acts as the “upper house.” However, the lawmaking process can begin in either house.

Why Does the United States Have a Bicameral Legislature?

The Articles of Confederation were created soon after the Declaration of Independence but did not go into effect until 1781. They created a federal government composed of an alliance of states. The Articles created a unicameral Congress made up of one delegate from each of the 13 colonies.

However, this lawmaking body was weak with no real authority to govern on a national level. Congress did not have the power to tax or regulate foreign or interstate commerce. Additionally, there was no executive to execute the laws Congress passed. There were attempts to strengthen the Articles but the states did not act, afraid of creating a Congress that would have more power than the states.

Given the failures of Congress under the Articles of Confederation, the framers of the Constitution wanted to create a powerful legislative body as part of the system of checks and balances. However, they, too, feared a single legislative body might be too powerful.

In order to address the form Congress would take, the framers looked to history, other countries, and to the states. Many of the historical republics studied by the founders had bicameral legislatures. Similarly, the United Kingdom had a bicameral parliament. Many states, however, had established unicameral systems after the Revolutionary war.

The founders considered this and determined that a two-chambered legislature would be the most advantageous. Two chambers would provide an additional layer of checks and balances within Congress. James Madison noted that bicameralism would create two “different bodies of men who might watch and check each other."

Creation of the Houses of Congress

Once the bicameral system had been accepted, the next problem was the makeup of the legislative chambers. This was very contentious and threatened to deadlock the Constitutional Convention.

Congress would be the states' representation in the federal government. The interests of the larger states, mainly in the South, were at odds with the interests of the smaller Northern states. The Virginia Plan proposed that both houses be apportioned based on the population of the states. This plan clearly favored the larger states. The smaller states understandably objected to this plan, wanting equal representation. Finally, the delegates accepted the Great Compromise, creating a bicameral legislature with representation by population in one house and equal representation in the other.

The Great Compromise determined that members of the House of Representatives would be apportioned based on the state's population. The representatives would be elected by popular vote in the states. The size of the House has changed as the population of the United States has grown. Today, the House is limited to 435 representatives, based on proportional representation by population. California is the largest state and has the most representatives with 53. States with the smallest population, such as Alaska and North Dakota, have only one representative.

The Senate was apportioned based on equal representation for the states. Each state, regardless of size, has two senators. Originally, electors from the state legislature selected senators. It was hoped that the appointed senators be more conservative and act as a check to the more populist House. However, the appointment of senators caused many problems, including vacant seats and corruption. The Seventeenth Amendment, ratified in 1913, allowed for the popular election of the senators. Today the Senate has 100 members. In the event of a tie in voting, the Vice President, serving as President of the Senate, will break the tie.

The Legislative Process Under Bicameralism

All legislative power is based in Congress. Only Congress has the power to change existing laws and create new laws. The process of making a law depends on bicameralism. In order to become law, a bill must pass through both the House of Representatives and the Senate in identical form. This can often take time.

A bill can be introduced in either house by a sponsoring representative or senator. After the bill is introduced, it goes to a committee that deals more specifically with those types of bills. After the bill passes the committee, it goes to the main body for a vote. Once it passes, the bill will be sent to the other house.

The bill that is advanced may not be in the same form as it was introduced, changes can be made and amendments added. Either body may make changes or amendments. If a bill passes one house but is amended by the other, it must be returned to the original house for approval.

Once both chambers have approved the bill, it can be sent to the executive branch and signed into law by the president. If the president vetoes the bill, the veto can be overridden by a 2/3 vote in each chamber.

Limited and Enumerated Powers

As an additional way to check Congress's power, the framers limited the power to those specifically enumerated in the Constitution. With each branch being granted certain separate powers the other did not possess.

House of Representatives

Because the House was made up of representatives directly elected based on the population of the states, it was seen as being closer to constituents. The powers the House was given reflect that, including the power to hold the purse strings. Under the Origination Clause, all bills for raising revenue must start in the house. These initiatives can be amended in the Senate but must always originate in the House.

Representatives also serve only two-year terms. This means they are almost always having to consider what their constituents want and what will get them re-elected.

The House possesses the power to impeach the President and other federal officials. And in the event of an Electoral College tie, the House has the power to elect the President. For example, during the 1824 election, no candidate received a majority of the electoral vote. The House held a contingent vote and John Quincy Adams became president without winning the popular or electoral vote.


The Senate has the power to confirm the President's appointments that require confirmation, for example, cabinet members, members of the Supreme Court, and the federal judiciary. However, if the Vice Presidency is vacant, the House of Representatives must also approve the appointment of the Vice President.

The Senate also tries impeachment cases sent by the House. Finally, the Senate provides advice and consent on and ratifies treaties (except for those that affect foreign trade, which must also have the approval of the House).

Senators have longer terms than U.S. Representatives, serving for six years instead of two before having to seek re-election.

Bicameralism created a powerful Congress but it also served as an additional layer of checks and balances. Other countries have set up bicameral legislatures based on the English and American models, creating large “first chambers” like the House of Representatives and smaller “second chambers” like the Senate. A bicameral model is most often used in countries with a national legislature, known in the U.S., Canada, and Australia as the federal legislature. Denmark employed a bicameral legislature for around a hundred years before switching to a single chamber model in 1953. Some countries refer to their legislative systems as “parliamentary systems.”

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