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The 8 types of formal fallacies (and examples)

The 8 types of formal fallacies (and examples)

July 19, 2024

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 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 that are 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 deceptive nature of these arguments.

But recognizing a fallacy is not easy, because it can take different forms. In fact, there are many types of fallacies, some of which do not resemble each other . It is important to know them well if you want to ensure the quality of the debates and the knowledge generation processes in a valid way. After all, a "mistake" can make the conclusion reached is completely wrong.


Formal and informal fallacies

The most general classification that can be made of fallacies is what distinguishes between formal fallacies and informal ones . While in the latter the reasoning error has to do with the content of the propositions, in the formal fallacies the reasoning error is in the way in which the propositions relate to each other. Therefore, formal fallacies are always objectively, while in the case of informal ones, a debate is generated about whether or not there is an argumentation error, given that 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 who says it is an ad hominem fallacy, but it is not the same 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 to try to mobbing. In the case of formal fallacies, there is no room for discussion, in any case you can examine if 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. Falacious disjunctive syllogism

In this fallacy part of a disjunction of the style "A and / or B" . When one of the possibilities is affirmed, it is assumed that the other is false. Of course, this conclusion does not derive from the premises.

Example : "You can eat or shower if you wish, you are showering, so you will not eat." This fallacy is not true 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 maximum grade, so if I take the maximum grade I will have studied a lot."

3. Denial of the antecedent

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

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

4. False denial of the 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, there has not been a good cake, therefore it has not been cream."

5. Average term not distributed

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 it occurs in any categorical syllogism in which both premises are a negation , since from them you can not conclude anything.

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 the categorical syllogisms you can not get a negative conclusion from affirmative premises , and to do it supposes to fall in a fallacious reasoning.

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

8. Fallacy of four terms

In this fallacy There are four terms, instead of three, which would be necessary to be valid . This happens because one of the terms has two meanings.

Example : "Man is the only animal capable of taming the fire, the woman is not a man, so the woman can not tame the fire."

31 logical fallacies in 8 minutes (July 2024).


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