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Introduction to Political Science

9.3 What Is the Difference between Unicameral and Bicameral Systems?

Introduction to Political Science9.3 What Is the Difference between Unicameral and Bicameral Systems?

Learning Outcomes

By the end of this section, you will be able to:

  • Define unicameral and bicameral legislature.
  • Outline which types of legislative systems exist in different parts of the world.
  • Analyze the relative advantages and disadvantages of each type of legislative system.

One key structural component of legislatures is the number of chambers that they have. The two most common options for chamber structure are unicameral and bicameral. A unicameral legislature has only one chamber, or body, that makes decisions. A bicameral legislature has two chambers, often with different procedures and powers, that ultimately must work together to make policy and exercise other legislative powers and responsibilities.

Strengths and Weaknesses of a Unicameral Legislature

One of the main strengths of unicameral legislatures is that they create a more efficient legislative process. In a unicameral legislature, bills only need to go before and be debated by one set of decision makers, whereas in a bicameral legislature, both chambers must debate and approve bills in order for them to have a chance of becoming laws. This legislative efficiency is particularly valued in more homogenous societies, where having venues for different voices and perspectives is not seen as particularly important. In these societies, political parties are considered sufficient to protect diverse interests.

Unicameral systems do not lend themselves to oversight and checks on the power of the legislature. In bicameral systems, the need to pass legislation through another chamber is a natural “veto point”; if there is support for legislation in one chamber but not the other, that may reflect broad concerns of a segment of the public, so the public’s preferences are better served when both chambers weigh in and consider a piece of legislation. The lack of a natural “veto point” is particularly apparent in unicameral parliamentary systems, where a prime minister with a strong governing majority faces almost no constraints from either a separate chamber or an effective minority opposition.

Strengths and Weaknesses of a Bicameral Legislature

Bicameral systems make up approximately one-half of legislatures around the world. Bicameralism is largely thought to allow the structures of a political system to reflect different voices and priorities. In bicameral systems, there is often a lower chamber, more closely associated with the perspective of the people, and an upper chamber, which might reflect different territories or classes.52 For example, in the German parliamentary system, the lower chamber, the Bundestag, is directly elected by the public, while the upper chamber, the Bundesrat, is supposed to represent the 16 Länder, or states. While each state has between three and six votes on legislation, all of a state’s votes in the Bundesrat must be cast as a bloc, either for or against a piece of legislation.53 The idea is that the vote should represent the state’s interests, not the interests of the individuals representing the state. The two chambers create a system of checks and balances within the legislative branch so that any legislation that can survive the legislative branch process is much more likely to succeed.

Young adult student journalists wearing lanyards sit facing forward in tiered rows of two-person desks.
Figure 9.13 Student journalists participate in a 2017 celebration of youth journalism taking place on the floor of the German Bundesrat. Note how the names of the Länder are affixed to the desks, highlighting the importance of representing a particular region. (credit: “Preisverleihung - SZWdL17” by Jugendpresse Deutschland/Timon Suhk/Flickr, CC BY 2.0)

There are important weaknesses to bicameral systems. First, the legislative process is inefficient. After a bill has been investigated, debated, and voted on in one chamber, it must go to a second chamber and complete the whole process again. This can both significantly extend the time it takes for a piece of legislation to pass and dramatically raise the odds that a piece of legislation will die before it gets to a vote, as at every stage along the way there are two sets of decision makers who can choose not to proceed with a piece of legislation. This phenomenon played a significant role in preventing comprehensive immigration reform in the United States in the first two decades of the 21st century. One nuance of the American legislative process is that bills that haven’t passed both chambers of Congress expire at the end of each two-year session. Although a number of different pieces of immigration legislation were introduced between 2000 and 2020, and some passed either the House or the Senate, no comprehensive immigration legislation was signed into law.54 Additionally, both chambers must pass the exact same text of legislation. As many systems allow both chambers to amend legislation, a piece of legislation can bounce back and forth between the two chambers until they can agree on a final version. That can also add significant time and inefficiencies to the legislative process.

Another weakness of bicameralism is that it can suffer from gridlock when different parties hold the majority in each chamber, particularly when the two parties in charge have significant policy and ideological disagreements.

The strengths and weaknesses of bicameralism are two sides of the same coin. A system that, by design, allows for more voices can become a system where nothing can happen, as disagreement in the legislature can cause everything to come to a screeching halt.

Show Me the Data

Frequency of Unicameral and Bicameral Legislatures around the World

A world map codes countries according to whether they have bicameral or unicameral legislatures, some variant, or no legislature at all.
Figure 9.14 Approximately half of the countries around the world have bicameral legislatures (in green), while the other half have unicameral legislatures (in blue). A few countries, for example China and Iran, have unicameral legislatures with separate advisory bodies (brown), and a couple others have no legislature at all (red). (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

A quick look around the world shows some interesting patterns. Many large countries have a bicameral legislative system. In part, this reflects the influence that the United States and European countries have around the globe. But a significant number of countries, including countries in western and southern Africa, Central America, the Middle East, and northern Europe, as well as many island nations, have unicameral legislatures. What characteristics do you think influence countries to adopt one structure of legislature versus the other?

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