Circular reasoning, also called begging the question (petitio principii), is an argument whose conclusion is already assumed in its premises: “this source is trustworthy because it says it is trustworthy”. As the Stanford Encyclopedia of Philosophy notes, the fallacy goes back to Aristotle, and its fault is not invalid logic: the premises simply give no independent support.
How it works
Where you see it today
Using a language model to judge outputs has become common, but researchers found that models can recognise their own text and score it higher than others’ work that humans rate as equal (Panickssery et al., 2024). A model that grades itself risks confirming what it already produced.
If test questions leaked into a model’s training data, a high score may partly measure memory of the test. Researchers have proposed ways to detect this contamination (Golchin and Surdeanu, 2023).
Using the same data both to pick what to look at and to test it can produce effects even in pure noise, a problem neuroscientists called circular analysis (Kriegeskorte et al., 2009). The same trap appears when an A/B test segment is chosen after seeing the results.
Asking a model whether its own answer is correct, and treating yes as confirmation, is a loop. Checking needs a source outside the model: a document, a test, a person.
Circular reasoning vs related ideas
How to spot and avoid it
- Restate the argument with the conclusion removed and see whether any support is left.
- Ask where each piece of evidence came from, and whether it depends on the claim itself.
- Do not let a model be the only judge of its own output; use a different evaluator, tests or human review.
- Keep a held-out data set that is never used to choose what to test.
- Be careful with definitions that make a claim true by construction.
AI evaluation can turn circular when models are trained on model-made data and judged by models with similar blind spots. The Business Engineer argues that tasks with outside, verifiable checks are the ones agents can take over first, because the check breaks the loop.
Read: What Can Be Benchmarked Can Be Made Autonomous →Explore the platform →Related: Begging the question · Confirmation bias · Appeal to authority · Straw man fallacy · Ad hominem
Frequently asked questions
What is circular reasoning?
It is an argument whose conclusion is already assumed in its premises, so it offers no independent support for the claim.
Is circular reasoning the same as begging the question?
Yes, in logic begging the question (<em>petitio principii</em>) means assuming what you set out to prove; in everyday speech the phrase is often used to mean “raises the question”.
Is a circular argument logically invalid?
Not necessarily: its form can be valid, but it fails as a proof because the premises depend on the conclusion.
How does circular reasoning affect AI evaluation?
When a model judges its own outputs, or is tested on data it saw in training, the result can confirm itself rather than measure real quality.
Sources
- Hansen (2015, revised 2024), Fallacies, Stanford Encyclopedia of Philosophy
- Panickssery, Bowman & Feng (2024), LLM Evaluators Recognize and Favor Their Own Generations
- Golchin & Surdeanu (2023), Time Travel in LLMs: Tracing Data Contamination in Large Language Models
- Kriegeskorte et al. (2009), Circular analysis in systems neuroscience: the dangers of double dipping, Nature Neuroscience
The full guide
The complete explainer, cleaned up and reformatted for mobile.
The circular reasoning fallacy, also known as circular logic or petitio principii, is a common flaw in reasoning where the argument’s conclusion is already contained within its premises, rendering the argument invalid. It’s a subtle and deceptive form of faulty logic that can easily mislead listeners or readers.
Defining the Circular Reasoning Fallacy
Circular reasoning occurs when an argument is structured in a way that assumes the truth of the conclusion within its premises, making it logically unsound. Instead of offering independent evidence or support for the conclusion, circular reasoning merely restates or rephrases the conclusion in a different form. It creates a circular or self-referential chain of reasoning that leads nowhere.
The structure of circular reasoning can be summarized as follows
- Premise 1 (P1): Contains the conclusion or an equivalent statement.
- Conclusion (C): Essentially restates P1.
- Therefore, C is true.
In this fallacy, the argument fails to provide any new information or logical progression from the premises to the conclusion. It assumes what it intends to prove, making it logically invalid.
Examples of the Circular Reasoning Fallacy
To better understand the circular reasoning fallacy, let’s examine some examples:
Example 1: “The book is reliable because it is trustworthy.”
In this example, the conclusion (“The book is reliable”) is essentially a rephrasing of the premise (“it is trustworthy”). The argument doesn’t offer any external evidence or criteria for why the book should be considered trustworthy, making it circular.
Example 2: “I know the answer is correct because I’m certain it’s right.”
This argument relies on the premise of personal certainty to support the conclusion that the answer is correct. However, it doesn’t provide any objective evidence or reasoning to demonstrate why the answer is right, resulting in circular reasoning.
Example 3: “Aliens must exist because there are countless reports of UFO sightings.”
In this case, the conclusion (“Aliens must exist”) is based on the premise of “countless reports of UFO sightings.” However, the argument doesn’t establish the credibility or validity of those reports, making it circular.
Identifying the Circular Reasoning Fallacy
Recognizing the circular reasoning fallacy can be challenging because it often involves a subtle and seemingly coherent presentation. Here are some key indicators to help identify circular reasoning:
- Repetition of Ideas: Look for arguments that repeat the same ideas or concepts between the premises and the conclusion. If the conclusion is a restatement of a premise, it may be circular.
- Assumption of Conclusion: Check if the premises assume the truth of the conclusion or rely on it to make sense. If the argument appears to take the conclusion for granted, it’s likely circular.
- Lack of Independent Support: Circular reasoning typically lacks independent evidence or logical steps to connect the premises to the conclusion. If the argument fails to provide new information or reasoning, it may be circular.
- Use of Circular Language: Pay attention to language that suggests circular reasoning, such as phrases like “because it’s true” or “since it’s correct.” These phrases often indicate circularity.
- Question the Validity: Ask whether the premises actually support the conclusion or if they merely restate it. If the premises don’t offer distinct reasons or evidence for the conclusion, circular reasoning is likely present.
Why Circular Reasoning Is a Fallacy
Circular reasoning is considered a fallacy for several reasons
- Logical Invalidity: Circular arguments lack logical validity because they don’t establish the truth of the conclusion. They create a circular structure where the conclusion is already assumed in the premises.
- No New Information: Circular reasoning fails to provide any new information, evidence, or reasoning that would contribute to the argument’s validity. It’s essentially a self-referential loop that adds no substance to the discussion.
- Deceptive Appearance: Circular reasoning can be deceptive because it may appear valid on the surface. People may mistake it for a convincing argument, leading to false beliefs or conclusions.
- Circular Chains: Circular reasoning can create chains of arguments that rely on each other’s circularity, making it difficult to break the loop and arrive at a valid conclusion.
Common Misconceptions
To avoid misconceptions, it’s important to clarify a few common points related to circular reasoning:
- Circular Definitions: Circular reasoning should not be confused with circular definitions. In some cases, circular definitions are necessary in the process of defining terms but are not the same as circular reasoning in argumentation.
- Complex Arguments: Circular reasoning can be found in both simple and complex arguments. A lengthy or complex argument can still be circular if it ultimately relies on a premise that assumes the conclusion.
Avoiding the Circular Reasoning Fallacy
To avoid using circular reasoning in your arguments and to recognize it in others’ reasoning, consider the following tips:
- Challenge Assumptions: Be aware of any assumptions you are making in your argument. Avoid premises that assume the conclusion.
- Seek External Evidence: Ensure that your premises provide external evidence or reasoning to support the conclusion. Strive for independent support.
- Use Critical Thinking: Encourage critical thinking and skepticism when evaluating arguments. Question whether the premises truly support the conclusion or if circular reasoning is at play.
- Seek Feedback: Share your arguments with others and seek feedback. Different perspectives can help identify circular reasoning.
- Improve Argument Structure: Refine the structure of your arguments to ensure logical validity. Avoid circular chains of reasoning.
Conclusion
The circular reasoning fallacy is a common and deceptive flaw in reasoning where the conclusion is already embedded within the premises, making the argument logically invalid. Recognizing and avoiding circular reasoning is essential for sound argumentation and critical thinking. By identifying circularity in arguments, we can engage in more productive and rational discussions, leading to better-informed conclusions and beliefs.
