A tautology is a grammatical construct; circular reasoning is a logical fallacy. The two phenomena are related but not identical.
A tautology is a sentence in which the conclusion is equivalent to its premise. In other words, in a tautology, the predicate can be surmised by reading the subject.
Here are some examples of tautologies:
My mother’s brother is my uncle.
Father Brown is a priest.
It is what it is.
A circular argument occurs when someone affirms her position simply by restating it in different terms. In other words, circular reasoning is an argument where the conclusion depends upon or is equivalent to its premise.
In a circular argument:
X is true because of Y.
and
Y is true because of X.
A circular argument is similar in structure to a tautology, but a circular argument includes causal reasoning (because, therefore, for this reason, etc.).
Here are some examples of circular reasoning:
My mom is terrific because she is wonderful.
People do what Dave tells; therefore, he is a great leader.
I slumbered beyond my assigned wakeup time; that’s why I overslept.
Lesson Evaluation: Explain why the following examples are tautologies, circular arguments, or neither.
Chris Rock is a hilarious comedian because he makes people laugh.
A bartender is a guy who listens to people talk all day.
Freedom’s just another word for nothing left to lose.
Anthony is extremely strong due to his ability to bench press three hundred pounds.
If aliens didn’t create the pyramids then how come pyramids are the product of technology that didn’t exist on earth at that time?
Allen hasn’t had a drink in twenty-three years, but he isn’t really sober because he doesn’t go to AA meetings and he isn’t working the steps.
A man’s gotta do what a man’s gotta do.
They are who we thought they were.
If I could tell you, I would let you know.
I stopped eating meat in 1987; that’s what makes me a vegetarian.
by Richard W. Bray
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