Circular reasoning, or begging the question, is a fallacy committed when one attempts to justify a claim using a premise whose truth is dependent upon the very claim one is trying to demonstrate. The archetypal example of this fallacy, itself likely an instance of a strawman argument, is the following argument for the inerrancy of the bible: “we can know that the bible is the word of God because god himself says so in the bible, and god does not lie.” This argument relies on the premise that God’s word can be found in the bible, which in turn requires that God exists, which is the very conclusion that the argument seeks to establish. As such, the argument will not be persuasive to anyone who does not already agree with its conclusion.
Circular reasoning is not false (since if a conclusion really is true it can be used as a premise); it is simply ineffective as a form of argument. Typically, a valid argument attempts to present a series of premises which entail the conclusion, and the truth of the premises must be able to be established independently of the conclusion. The objective is to establish the truth of the premises independently of the conclusion, and therefore render it impossible (or at least very difficult) to dispute the truth of the conclusion, since one cannot simultaneously accept the premises of a valid argument and deny its conclusion. In the case of a circular argument, however, all one need do is deny the conclusion, since one or more of the premises depend upon the conclusion for their support, and therefore denying the conclusion alone is sufficient for rejection of the entire argument. This is what makes circular arguments so useless; they can be denied without any analysis or argument, simply by denying the conclusion.
Real examples of circular reasoning are typically more subtle than the example given above, and generally involve arguments that sound plausible, but upon closer examination turn out to appeal to their own conclusions in order to establish the truth of their premises. This often occurs in discussions of moral issues. Consider these two examples:
“Women have the right to control what happens to their own body, and abortion concerns control over a women’s body, therefore women should have a right to access abortion.”
“A baby has the right to life, a right which is unjustly denied by an abortion, therefore abortion should remain against the law.”
In both cases the initial principles of a ‘right to control her own body’ and a ‘right to life’ may sound plausible, however on closer inspection it is clear that whether or not one accepts these principles will depend upon one’s stance on abortion. Those who believe that abortion is permissible will deny that all prenatal babies have an unconditional ‘right to life’, while on the other hand those who oppose abortion will deny that all women have an unconditional right to control over their own body in all circumstances. Thus in both cases the reasoning is circular, in that the truth of one of the premises is ultimately dependent upon the truth of the conclusion attempting to be established.
Begging the question: overview from Logical Fallacies
Begging the question: overview from the Nizkor Project
Begging the question: overview from Logically Fallacious
Begging the question: overview from Fallacy Files