These fallacies have in common a general failure to prove that the conclusion is true.

The truth of the conclusion is assumed by the premises. Often, the conclusion is simply restated in the premises in a slightly different form. In more difficult cases, the premise is a consequence of the conclusion. "To beg the question is to assume its truth or falsity without proof. This does not mean a direct assumption of truth or falsity but an indirect assumption reached in a circuitous manner by an appearance of logical reasoning. In logic this error is called petitio principi. It may appear in many different forms but the following are the most frequently encountered: A. Arguing in a circle. This error involves more than one syllogism. It begins by assuming the truth of a premise, next upon this premise a conclusion is built and then finally this very conclusion is used in an attempt to prove the premise with which the syllogism was begun. ... B. Directly assuming the point at issue. In directly assuming the truth of the point at issue much language is employed which tends to conceal the lack of real proof. Stripped of their wealth of expression such so-called arguments appear as bare unsupported assertions." (Ketcham, Theory and Practice of Argumentation and Debate, pp. 250-1)

An argument which purports to prove one thing instead proves a different conclusion.

The author attacks an argument which is different from, and usually weaker than, the opposition's best argument.