circular argument

circular argument, logical fallacy in which the premise of an argument assumes the conclusion to be true.

A circular argument’s premise explicitly or implicitly assumes that its conclusion is true rather than providing any supporting statements. If the conclusion and premise were switched, the statement would still stand as “proven.” For example, “Alex is a cheerful person because he is always in a good mood.” Both parts of the argument state the same information: Alex’s constant good mood is equated with being a cheerful person. The argument gives no reasoning as to why Alex is a cheerful person. Another example is “Statistics is a useless course and should be dropped from high-school curricula.” That statistics is useless is assumed. However, the argument has not proven this statement. While a circular argument can be a valid argument if both its premise and its conclusion are true, it is a fallacious argument in that it does not stand the test of good reasoning because its premise and conclusion are identical.

The idea of a circular argument first appeared in Aristotle’s Metaphysics (350 bce) as τὸ ἐξ ἀρχῆς αἰτεῖν (to ex arches aitein). The Greek phrase means “an assumption at the outset.” Its Latin equivalent, petitio principii, used in formal applications of logic, is a direct translation of the original Greek—petitio meaning “assumption” and principii meaning “from the beginning.” In informal contexts, the phrase begging the question (to take for granted without providing reasoning) is often used for circular arguments. However, in colloquial English, the phrase is often used incorrectly to mean “raising the question.”

Closely related to begging the question is circular reasoning (Latin: circulus in probando, “circle in proving”). Some consider circular reasoning to be the same as petitio principii, but circular reasoning is defined as two or more arguments in a chain format, such as “Earth is flat. If it were not flat, someone would show us a picture of it. That picture of Earth doesn’t show something real because it shows Earth as a sphere and not flat. In conclusion, Earth is flat.” Circular reasoning is thus most often considered one form of petitio principii. A famous example of a circular argument is the paradoxical response to the question “Which came first—the chicken or the egg?” The argument usually goes something like this: “Chickens hatch from eggs, but an egg does not exist unless a chicken lays it, and yet a chicken must hatch from an egg” and so on.

There are several other forms of petitio principii. One form is the immediate argument (hysteron proteron), a basic premise and conclusion, which follows the structure “Statement a′ is true; therefore, statement a is true” (“Diamonds are worth a lot because they are expensive”). Immediate arguments may include epithets that beg the question or certain phrases that present an abstract conclusion already provided by a concrete premise (“The judge is just and fair because he sets the innocent free and punishes the guilty”). Another form of circular argument is the grammatical or logical immediate inference structure: “Statement a is true; therefore, statement not-a is not true” (“People who fail out of school do so because they are not smart, and they are not smart because they fail out of school”). Sometimes a speaker provides an argument that simply repeats the words of its premise in its conclusion (“It’s bad because it’s bad”).