The 8 Types Of Formal Fallacies (and Examples)

Gaps and dialectical biases that turn our argument into a falsehood.

In the world of  philosophy and psychology, the concept of fallacy is very important, because it gives an idea of ​​the quality of reasoning that we can use to argue a point of view.

What is a fallacy? It is simply a reasoning error, a type of argumentation in which the premises used do not lead to the conclusion. In fact, the term is derived from the word “fallare”, which means to lie or cheat. That is, it serves to emphasize the misleading nature of these reasonings.

But recognizing a fallacy is not easy, because it can take different forms. In fact , there are many types of fallacies, some of which look nothing like each other. It is important to know them well if you want to ensure the quality of the debates and knowledge generation processes in a valid way. Ultimately, a “mistake” can make the conclusion reached totally wrong.

Formal and informal fallacies

The most general classification that can be made of the fallacies is the one that distinguishes between formal and informal fallacies. While in the latter the error of reasoning has to do with the content of the propositions, in the formal fallacies the error of reasoning is in the way in which the propositions are related to each other. Consequently, formal fallacies are always objectively so, while in the case of informal ones, a debate may arise about whether or not there is an error in argumentation, since their nature always depends on the context in which they are used.

For example, trying to discredit an idea by talking about the negative aspects of the person who says it is an ad hominem fallacy, but the same is not the case if talking about the person who argues gives relevant information that should be brought up. If the person who decides to focus the debate on the misconduct of a worker is known for trying to mob him . In the case of formal fallacies, there is no room for discussion, in any case it is possible to examine whether the concepts used are correct (for example, if the same word has two different meanings throughout the logical operation).

In this article we will focus on analyzing the types of formal fallacies. To know more about the types of fallacies in general, you can visit this article.

Types of formal fallacies and examples

Next we will review the main types of formal fallacies.

1. False disjunctive syllogism

In this fallacy, one starts from a disjunction of the style “A and / or B”. When one of the possibilities is affirmed, the other is assumed to be false. Of course, this conclusion does not follow from the premises.

Example : “You can eat or shower if you wish. You are taking a shower, so you are not going to eat. This fallacy is not such when the disjunction is exclusive:” or A or B “.”

2. Affirmation of the consequent

In this formal fallacy it is assumed that if a premise is true, then the consequence of this premise also indicates whether its predecessor is true or not.

Example : “If I study a lot I will get the highest grade, so if I get the highest grade I will have studied a lot.”

3. Denial of antecedent

In this kind of formal fallacy the reasoning is articulated as if denying a premise the conclusion of the premise had to be necessarily false.

Example : “If it rains, the street will get wet; it hasn’t rained, so the street won’t get wet.”

4. False denial of the conjunction

This fallacy occurs when a phenomenon does not occur as a result of a set of elements, one of those elements is denied.

Example : “To make a good cake you need flour and cream; a good cake has not remained, therefore no cream has been added.”

5. Undistributed middle term

In this fallacy there is an element that connects two others and that does not appear in the conclusion, although one of them does not include it in its entirety.

Example : “All mammals have eyes, some mollusks have eyes, therefore some mollusks are mammals.”

6. Categorical syllogism with negative premises

This fallacy occurs in any categorical syllogism in which both premises are a negation, since nothing can be concluded from them.

Example : “No mammal has feathers, no mouse has feathers, so no mammal is a mouse.”

7. Categorical syllogism with negative conclusion from affirmative premises

In categorical syllogisms , a negative conclusion cannot be obtained from affirmative premises, and doing so implies falling into fallacious reasoning.

Example : “All Germans are European and some Christians are European, so Christians are not German.”

8. Four-term fallacy

In this fallacy there are four terms, instead of three, that would be necessary for it to be valid. This occurs because one of the terms has two meanings.

Example : “Man is the only animal capable of taming fire, woman is not a man, so woman cannot tame fire.”

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