一般的邏輯教科書大部分都會介紹各色各樣的非形式謬誤（Informal Fallacy）。筆者認為其中的一些謬誤的定義似乎有混淆不精確之處，而有重新檢討的必要。由於非形式謬誤的種類很多，本文只討論「人身攻擊的謬誤」（Argumentum ad Hominem）；（二）「竊取論點（或譯「丐問」）的謬誤」（petitio Principii；Fallacy of begging the Question）。筆者認為「人身攻擊的謬誤」一詞不當，宜改成「離題的謬論」（The Beside Point fallacy），因為這一詞很容易讓人望文生義，而誤作「不可作人身攻擊」。其次，有關循環論證是否有效的問題。筆者認為，那要看一種意義下的「循環論證」而定。如果「竊取論點的謬誤」是「循環論證」的特例，則「循環論證」有些有效、有些無效。反之，如果「循環論證」是「竊取論點的謬誤」的特例，則「循環論證」是有效的。筆者認為後者比較有說服力。
Most introductory logic textbooks contain a section on informal fallacies. I think some of these fallacies are nor clearly and precisely defined, and call fo re-examination. In this paper I will deal with two of them (1) Argumentum ad Hominem, and (2) Petitio Principii (Begging the Question) I believe the term ‘Argumentum ad Hominem ‘is misleading because it is misleading because it is often wrongly interpreted as ‘Attack on the Personal Character of the opponent’ I suggest the name be changed to ‘Beside the point fallacy’. As to the validity of the ‘Circular Argument’, I think it depends on how on defines it. We can define ‘Begging the Question’ as an example of ‘Circular Argument, then it can be either valid or invalid. On the other hand, we can define ‘circular Argument’ as an example of’Begging the Question’, then it is valid. I think the latter is more acceptable.
