The Logical Fallacy of Circular Arguments
A circular argument is really just a special form of begging the question. It
occurs when a premise of an argument presupposes the truth of the conclusion.
Premises are supposed to give us reasons for believing the conclusion is true, not
take the truth of the conclusion for granted right from the start. So the test for
circularity is this: In deciding that a given premise is true, did you have to
assume the conclusion was already known to be true? Then the argument
merely goes in a circle and proves nothing. Some examples:
1. Someone asks `Why is Sammy so afraid of heights?' You explain `Because he
has acrophobia'. Your argument is circular. `Acrophobia' means fear of heights.
So the premise presupposes the conclusion is true. A really good argument
would explain why Sammy has acrophobia.
2. Some folks have been heard to say `People who commit cold-blooded murder
are insane'. What is their evidence of this? Sometimes it turns out that they
simply think it is true by definition that anyone who commits cold-blooded
murder is insane. In other words, they define `insanity' in a way that
guarantees anyone who commits cold-blooded murder is insane. That eliminates
any need to actually examine cold-blooded murderers for signs of mental illness.
3. In the debate over evolution vs. creationism, some creationists dismiss
Darwin's work as "just a theory". If we take this argument seriously, they must
be assuming that a theory is nothing more than an unproven hypothesis. So
their argument amounts to this:
Darwin's account of evolution is just a theory.
A theory is an unproven hypothesis.
So, there is no compelling reason to believe Darwin's theory.
But this is an uninteresting circular argument. Of course we have no good
reason to believe a theory if it is nothing more than an unproven hypothesis.
What they ignore is the fact that some theories are very well-confirmed, for
example, the germ theory of disease, or Newton's theory of gravitation. The
really interesting question is how well-confirmed Darwin's theory is, a matter that
the foregoing argument ignores altogether.