Circular reasoning
Circular reasoning is an argument in which the conclusion is already contained in the premises, so the argument gives you no reason to believe the conclusion unless you believed it before you started. Nothing in it is false and nothing in it is invalid. It simply does no work.
What circular reasoning is
Circular reasoning is an informal fallacy in which the support offered for a claim depends on that claim. What distinguishes it from its siblings among the logical fallacies is a strange property: a circular argument is valid. If the premises are true the conclusion must be true, because the conclusion is one of the premises. The failure is not in the logic, it is in the argument's purpose. An argument exists to move a reader from something they accept to something they do not, and a circle never leaves the starting point.
Two forms appear in practice. The tight circle repeats the claim in different words: "The instructions are clear because anyone can understand them." The wide circle runs through two or more steps that eventually return: the register is accurate because the auditor approved it, and the auditor is trustworthy because the register has always matched. Wide circles are harder to spot, and 3 or 4 steps is usually enough to make one invisible in conversation.
The shortest accurate definition, and what circular reasoning involves
The shortest accurate definition is one clause: the conclusion is doing the job of the evidence. Circular reasoning involves assuming what you set out to prove, either openly, by restating it, or quietly, by relying on a premise that only someone who already accepted the conclusion would grant.
The quiet version is the more common and the more damaging. Consider: "The safety checklist covers everything important, because every incident we have recorded was something on the checklist." The premise sounds like independent evidence and is not, since incidents are recorded using the checklist. Anything the checklist omits was never counted. The support is generated by the thing it is supposed to support, which is a circle drawn through a filing system rather than through a sentence.
The form it takes, in three shapes
Three shapes cover almost every circular argument you will meet.
- Restatement. The premise is a synonym of the conclusion. "This process is efficient because it wastes no time."
- Mutual support. Two claims lean on each other. "The gauge is calibrated because the readings look right, and the readings look right because the gauge is calibrated."
- Buried assumption. A definition, a category or a source is chosen so the conclusion cannot fail. "Every reliable supplier delivers on time, and this supplier delivers on time, so it is reliable" is circular if reliable was defined by punctuality in the first place.
The buried assumption shape connects to a related fallacy, no true Scotsman, where a counterexample is excluded by redefining the category. The definition is adjusted until the conclusion is guaranteed, which is circularity applied to vocabulary.
A worked example, and the repair
Here is a worked example with the repair. A workshop is arguing about a torque wrench. One technician says: "The wrench is accurate. I know because I checked 3 bolts with it and they all came out at the right torque." He checked them with the same wrench.
Written as three lines, the circle is plain:
- Premise: the wrench reported the correct torque on 3 bolts.
- Hidden premise: the wrench reports correctly.
- Conclusion: the wrench reports correctly.
The repair is always the same and it is always the same shape: bring in a source that does not depend on the conclusion. For the wrench, that means a calibration rig, a second wrench of a different make, or a known reference weight on a known lever arm. The test of the repair is one question: could this new source have produced a result that contradicted the claim? If it could not, you have widened the circle rather than broken it. This is the same discipline that separates confirmation from testing throughout skeptical thinking.
What circular reasoning is confused with: begging the question
Circular reasoning is confused with begging the question more than with anything else, and no, the 2 are not quite the same, though they overlap enough that many writers treat them as synonyms. Circular reasoning is the wider category; begging the question is the classical name for the specific move of assuming the point at issue.
| Circular reasoning | Begging the question | |
|---|---|---|
| What it names | Any argument whose support depends on its conclusion | Assuming the disputed point as a premise |
| Origin of the name | Modern description of the shape | Petitio principii, a Latin rendering of Aristotle's phrase for asking for the initial thing |
| Typical size | Often several steps | Often a single premise |
| Example | "A supports B, B supports C, C supports A." | "Overtime is unnecessary, since nobody needs to work extra hours." |
How is begging the question different from circular reasoning in practice? Begging the question can occur in a single sentence with no visible loop, because the disputed claim is smuggled in as an assumption rather than stated twice. Circular reasoning describes the completed loop. Every question begged is circular; not every circle is a single begged premise.
One caution about the phrase itself. In ordinary modern usage "begs the question" is frequently used to mean "raises the question", which is a different thing entirely. Both usages are now common in media, so when you meet the phrase, check which one is meant before you diagnose anything.
When an argument may legitimately assume its starting point
Assuming a starting point is not always a fault, and three cases are legitimate.
- State an axiom openly. Deductive systems begin with premises that are not proved inside the system. Geometry assumes its axioms and says so. What makes an assumption respectable is that it is declared and available for challenge, not that it is derived.
- Argue from shared premises. If both parties accept a rule, using it is not circular, even though neither has proved it in the conversation. This is how most practical reasoning proceeds.
- Reason inside a framework deliberately. "Given the current contract terms, this invoice is due on the fifteenth" assumes the contract. That is a conditional conclusion, honestly labeled.
There is a deeper limit here worth stating plainly. The ancient skeptics recorded an argument, transmitted through Sextus Empiricus and associated with Agrippa, that every attempt to justify a belief ends in one of three places: an infinite regress, a circle, or an assumption taken as given. Justification has to stop somewhere. What the fallacy of circular reasoning identifies is not the existence of assumptions but a circle disguised as evidence, offered to someone who does not already share it. Compare this with the way deductive and inductive reasoning handle their starting points, which is the honest version of the same problem.
The test to run on the next justification you hear
Run this test on any claim that comes with a reason attached. Ask: would someone who currently disagrees accept this premise, or does accepting it already require accepting the conclusion?
Then run the harder version on your own beliefs, because circular reasoning is much easier to spot in other people. Take something you are confident about, write down your single best reason for it, and ask: where did that reason come from, and could it have come out differently? If every source of your evidence was selected, filtered or interpreted by the belief itself, you have a circle, and no amount of additional confidence will break it. Only a source that could have contradicted you will do that.
Begging the question in everyday English
One more thing is worth knowing about this fallacy, because it causes more confusion than the fallacy itself: the phrase begs the question now carries two incompatible meanings in ordinary English.
The logical sense is the one described on this page: an argument assumes the very point in dispute. The everyday sense, now far more common in journalism and conversation, is "raises the question", as in "the delivery arrived empty, which begs the question of who packed it". Nothing circular is happening there. A question is simply being prompted.
Two practical consequences follow. When you meet the phrase in something you are reading, check which sense is intended before you diagnose a fallacy, because in most cases it is the second. And when you want to point out real circularity in your own writing, do not rely on the phrase to carry the meaning. Say what is actually wrong: "that premise assumes the thing we are trying to establish." The sentence is longer, it cannot be misread, and it names the fault instead of naming a label.