A，B和C代表什么并不重要 – 我们可以用“葡萄酒”，“牛奶”和“饮料”代替它们。该论点仍然无效，原因完全相同。如您所见，减少其结构的参数并忽略内容以查看它是否有效可能会有所帮助。

A = B.
B = C.
A = C.

Fallacies are defects in an argument – other than false premises – which cause an argument to be invalid, unsound or weak. Fallacies can be separated into two general groups: formal and informal. A formal fallacy is a defect which can be identified merely by looking at the logical structure of an argument rather than any specific statements. Informal fallacies are defects which can be identified only through an analysis of the actual content of the argument. Formal fallacies are only found only in deductive arguments with identifiable forms. One of the things which makes them appear reasonable is the fact that they look like and mimic valid logical arguments, but are in fact invalid. Here is an example:
All humans are mammals. (premise)
All cats are mammals. (premise)
All humans are cats. (conclusion)
Both premises in this argument are true but the conclusion is false. The defect is a formal fallacy, and can be demonstrated by reducing the argument to its bare structure:
All A are C
All B are C
All A are B
It does not matter what A, B, and C stand for — we could replace them with “wines,” “milk” and “beverages.” The argument would still be invalid and for the exact same reason. As you see, it can be helpful to reduce an argument to its structure and ignore content in order to see if it is valid.
Informal Fallacies
Informal fallacies are defects which can be identified only through an analysis of the actual content of the argument rather than through its structure.Here is an example:
Geological events produce rock. (premise)
Rock is a type of music. (premise)
Geological events produce music. (conclusion)
The premises in this argument are true, but clearly, the conclusion is false. Is the defect a formal fallacy or an informal fallacy? To see if this is actually a formal fallacy, we have to break it down to its basic structure:
A = B
B = C
A = C
This structure is valid; therefore the defect cannot be a formal fallacy and must instead be an informal fallacy identifiable from the content. When we examine the content we find that a key term, “rock,” is being used with two different definitions (the technical term for this sort of fallacy is ). Informal fallacies can work in several ways. Some distract the reader from what is really going on. Some, like in the above example, make use of or ambiguity to cause confusion. Some appeal to rather than logic and reason.