Unfortunately, people usually do not make it so easy to tell when they reason in a circle. Often, circular reasoning is disguised by restating the con- clusion in different words. Someone might argue that terrorists can’t be stopped without torture, because, if you do not use torture, there is no other way to stop terrorists. This premise means the same as the conclusion, so this reasoning is still circular.
Another way to hide circularity is by suppressing the premise that repeats the conclusion. Suppose someone argues that terrorists cannot be stopped without torture, because they are so callous that their goal is to kill and maim innocent civilians. This argument depends on the suppressed premise that anyone whose goal is to kill and maim innocent civilians cannot be stopped without tor- ture. If terrorists are then defined as people whose goal is to kill and maim innocent civilians, then this suppressed premise reduces to the conclusion that terrorists cannot be stopped without torture. So this argument is also circular.
Yet another trick is to put forward a statement first as a conclusion to be proved, and then only much later—after several subarguments or tangents—use the same statement as a premise on its own behalf. Consider this simple argument:
The only way to prevent terrorists from committing their horrible crimes is to inflict enough pain on them either to scare them off or to force them to reveal infor- mation that enables the police to head off terrorist attacks. Because these are the only methods that work, we cannot reason with them or talk them into giving up. We cannot make friends or sign a treaty with them. We cannot buy them off or sat- isfy their demands. Therefore, terrorists cannot be stopped without torture.
If the first sentence is supposed to provide a reason for the next three sentences, then those three sentences cannot later be used as a reason for the last sentence without the whole argument becoming circular, because the last sen- tence, “Terrorists can’t be stopped without torture,” means pretty much the same as the first sentence, “The only way to prevent terrorists . . . is to inflict enough pain on them. . . .” Although this trick is often harder to detect in a long and complex argument, such reasoning is still indirectly circular if any premise in a chain of arguments repeats or restates the eventual conclusion. Thus, we have circular reasoning if and only if one of the premises that is used directly or indirectly to support a conclusion is equivalent to the conclusion itself.