谬误是论证中的缺陷 – 除了错误的前提 – 导致论证无效，不健全或弱。谬误可以分为两大类：正式和非正式。正式的谬误是一种缺陷，只能通过查看参数的逻辑结构而不是任何特定的陈述来识别。非正式谬误是一种缺陷，只有通过分析论证的实际内容才能确定。正式谬误只能在具有可识别形式的演绎论证中找到。使它们显得合理的一个原因是它们看起来像模仿有效的逻辑参数，但实际上是无效的。这是一个例子：
所有人都是哺乳动物。 （前提）
所有猫都是哺乳动物。 （前提）
所有人都是猫。 （结论）
这个论点中的两个前提都是正确的，但结论是错误的。缺陷是一种正式的谬误，可以通过减少其裸结构的论证来证明：
所有A都是C.
所有B都是C.
所有A都是B.
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。
非正式的谬误
非正式谬误是一种缺陷，只能通过分析论证的实际内容而不是通过其结构来识别。这里是一个例子：
地质事件产生岩石。 （前提）
摇滚是一种音乐。 （前提）
地质活动产生音乐。 （结论）
这个论点中的前提是正确的，但很明显，结论是错误的。缺陷是正式的谬误还是非正式的谬误？要看这是否真的是一个正式的谬误，我们必须将其分解为基本结构：
A = B.
B = C.
A = C.
这种结构是有效的;因此，缺陷不能成为正式的谬误，而必须是从内容中可识别的非正式谬误。当我们检查内容时，我们发现一个关键术语“摇滚”正在使用两种不同的定义（这种谬误的技术术语是）。非正式谬误可以通过多种方式发挥作用。有些人会分散读者对真实情况的注意力。有些像上面的例子那样利用或模糊来引起混淆。有些人呼吁而不是逻辑和理性。
新加坡国立大学哲学系Essay代写:什么是逻辑谬误
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.