Arrow’s Impossibility Theorem


Arrow's Impossibility Theorem is a fundamental concept in social choice theory that challenges the idea of finding a perfect voting system. Developed by economist Kenneth Arrow in 1950, this theorem highlights the inherent difficulties in designing a voting system that satisfies a set of desirable criteria. In this article, we will explore the key insights of Arrow's Impossibility Theorem, its implications for democracy, and its relevance in modern society.

The Basics of Arrow's Impossibility Theorem

Arrow's Impossibility Theorem addresses the problem of aggregating individual preferences into a collective decision. It states that no voting system can simultaneously meet three seemingly reasonable criteria:

  1. Unrestricted Domain: The voting system should allow any possible set of individual preferences to be considered.
  2. Pareto Efficiency: If every individual prefers option A to option B, then the collective decision should also prefer A to B.
  3. Independence of Irrelevant Alternatives: The ranking of two options should not be affected by the inclusion or exclusion of a third, irrelevant option.

Arrow's theorem mathematically proves that it is impossible to design a voting system that satisfies all three criteria simultaneously. This means that any voting system will inevitably have some flaws or limitations.

Implications for Democracy

Arrow's Impossibility Theorem has significant implications for democratic decision-making processes. It challenges the notion of finding a perfect voting system that accurately reflects the will of the people.

One of the key implications is the vulnerability of voting systems to strategic manipulation. Since no system can be perfect, individuals or groups can strategically manipulate the outcome by strategically voting or influencing the agenda. This raises concerns about the fairness and integrity of the democratic process.

Additionally, Arrow's theorem highlights the difficulty of aggregating diverse preferences into a single decision. In a society with multiple conflicting interests, it becomes challenging to find a voting system that can accurately represent the preferences of all individuals. This can lead to dissatisfaction and a sense of exclusion among certain groups.

Real-World Examples

Arrow's Impossibility Theorem can be observed in various real-world scenarios. Let's explore a couple of examples to understand its practical implications:

Example 1: Brexit Referendum

The Brexit referendum held in the United Kingdom in 2016 provides an interesting case study. The referendum asked voters whether the UK should leave or remain in the European Union. The voting system used was a simple majority rule, where the option with the most votes would prevail.

However, Arrow's theorem suggests that this voting system is flawed. The referendum presented a complex issue with multiple dimensions, such as economic considerations, immigration policies, and sovereignty. Different individuals had different priorities and preferences, making it challenging to aggregate their preferences into a single decision.

Moreover, the inclusion of a third option, such as a “soft Brexit” or a “Norway model,” could have influenced the ranking between “leave” and “remain.” This violates the independence of irrelevant alternatives criterion of Arrow's theorem.

Example 2: Presidential Elections

Presidential elections in many countries also illustrate the challenges posed by Arrow's Impossibility Theorem. In a multi-candidate race, it becomes difficult to determine the true preferences of the electorate.

Consider a scenario where three candidates, A, B, and C, are running for president. The voting system used is a plurality voting system, where the candidate with the most votes wins. However, this system fails to capture the nuanced preferences of voters.

For instance, if the supporters of candidate C prefer candidate B over candidate A, their preferences are not reflected in the final outcome. This violates the Pareto efficiency criterion of Arrow's theorem, as the collective decision does not align with the preferences of a significant portion of the electorate.

Relevance in Modern Society

Arrow's Impossibility Theorem remains highly relevant in modern society, especially in the context of decision-making processes and policy formulation. Understanding its implications can help us design better voting systems and improve democratic practices.

One possible solution to address the limitations of voting systems is the use of ranked-choice voting. This system allows voters to rank candidates in order of preference. It eliminates the need for strategic voting and provides a more accurate representation of individual preferences.

Moreover, Arrow's theorem emphasizes the importance of transparency and accountability in decision-making processes. By ensuring that the decision-making process is fair, inclusive, and free from manipulation, we can mitigate some of the challenges posed by Arrow's Impossibility Theorem.


Arrow's Impossibility Theorem serves as a reminder that finding a perfect voting system is an elusive goal. It highlights the inherent difficulties in aggregating individual preferences into a collective decision and challenges the idea of a flawless democracy.

While Arrow's theorem may seem discouraging, it also encourages us to critically examine our voting systems and democratic practices. By understanding its implications, we can strive to design more inclusive and representative decision-making processes that better reflect the will of the people.

Ultimately, Arrow's Impossibility Theorem reminds us that democracy is a complex and evolving concept, and continuous efforts are needed to improve its functioning and ensure that the voices of all individuals are heard and respected.

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