The 8 types of formal fallacies (and examples)

Dialectical gaps and 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 the reasoning we can use to argue a point of view.

What is a fallacy? It is, quite simply, an error in reasoning, 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 deceive. That is, it serves to emphasize the deceptive character of these reasonings.

But recognizing a fallacy is not simple, because it can take different forms. In fact**, there are many types of fallacies, some of which do not resemble each other at all**. It is important to know them well if we want to ensure the quality of debates and knowledge generation processes in a valid way. At the end of the day, a "mistake" can make the conclusion reached totally erroneous.

Formal and informal fallacies

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

For example, trying to discredit an idea by talking about negative aspects of the speaker is an ad hominem fallacy, but the same is not true if talking about the person arguing 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 learn more about types of fallacies in general, you can visit this article.

Types of formal fallacies and examples

The following is an overview of the main types of formal fallacies.

1. Disjunctive fallacious syllogism

This fallacy is based on an "A and/or B" disjunction.. When one of the possibilities is affirmed, the other is assumed to be false. Of course, this conclusion does not follow from the premises.

• ExampleExample: "You can eat or take a 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: "either A or B"."

2. Assertion of the consequent

In this formal fallacy, it is assumed that if a premise is truethen the consequent of this premise also points out whether its antecedent is true or not.

• Example"If I study hard I will get the highest grade, so if I get the highest grade I will have studied hard".

3. negation of the antecedent

In this kind of formal fallacy the reasoning is articulated as if by negating a premise, the conclusion of this premise must necessarily be false..

• Example: "If it rains, the street will get wet; it has not rained, so the street will not get wet."

4. False negation of conjunction

This fallacy occurs when 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; it has not turned out to be a good cake, therefore no cream has been put in."

5. Undistributed mean term

In this fallacy there is an element that connects two others and that does not appear in the conclusionalthough one of them is not included in its totality.

• 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 negationsince 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 it is not possible to obtain a negative conclusion from affirmative premisesand to do so is to fall into fallacious reasoning.

• Example: "All Germans are Europeans and some Christians are Europeans, so Christians are not Germans."

8. Four-term fallacy

In this fallacy there are four terms, instead of three, which 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."