The 10 types of logical and argumentative fallacies

Philosophy and psychology are related to each other in many ways, among other things because they both approach the world of thought and ideas in one way or another.

One of these points of union between both disciplines is in relation to logical and argumentative fallacies,  concepts used to refer to the validity (or lack thereof) of the conclusions reached in a dialogue or debate. Let’s see in more detail what they consist of and what are the main types of fallacies.

What are fallacies?

A fallacy is a reasoning that although it looks like a valid argument, it is not .

It is, therefore, a line of reasoning that is erroneous, and the inferences that are presented as a product of these cannot be accepted. Regardless of whether the conclusion reached through a fallacy is true or not (it could be by pure chance), the process by which it has been reached is defective, because it violates at least one logical rule.

Fallacies and psychology

In the history of psychology there has almost always been a tendency to overestimate our ability to think rationally, being subject to logical rules and showing us coherent in our way of acting and arguing.

With the exception of certain psychological currents such as the psychoanalytic one founded by Sigmund Freud , it has been taken for granted that the healthy adult human being works according to a series of motives and reasonings that can be easily expressed verbatim and that normally fall within the framework of rationality. Cases in which someone behaved in an irrational manner were interpreted either as a sign of weakness or as an example in which the person does not know how to identify the true reasons that motivate their actions.

It has been in recent decades when you s and has begun to accept the idea that irrational behavior is located in the center of our lives , that rationality is the exception, not the reverse. However, there is a reality that has already been giving us a clue as to the extent to which we move by emotions and impulses that are little or not at all rational. This fact is that we have had to develop a kind of catalog of fallacies to try to make them have little weight in our daily lives.

The world of fallacies belongs more to the world of philosophy and epistemology than to that of psychology, but while philosophy studies the fallacies themselves, from psychology it is possible to investigate the way in which they are used. The fact of seeing to what extent the false arguments are present in the discourses of people and organizations gives us an idea of ​​the way in which the thinking behind them more or less conforms to the paradigm of rationality.

The main types of fallacies

The list of fallacies is very long and possibly there are some of them that have not yet been discovered because they exist in very minority or little studied cultures. However, there are some more common than others, so  knowing the main types of fallacies can serve as a reference to detect violations in the line of reasoning  where they occur.

Below you can see a compilation of the best known fallacies. As there is no single way to classify them to create a system of types of fallacies, in this case they are classified according to their belonging to two relatively easy to understand categories: non-formal and formal.

  1. Non-formal fallacies

Non-formal fallacies are those in which the reasoning error has to do with the content of the premises . In these types of fallacies, what is expressed in the premises does not allow us to reach the conclusion that has been reached, regardless of whether the premises are true or not.

In other words, irrational ideas about how the world works are appealed to to give the feeling that what is being said is true.

1.1. Fallacy ad ignorantiam

The ad ignorantiam fallacy attempts to take for granted the veracity of an idea simply because it cannot be shown to be false .

The famous Flying Spaghetti Monster meme is based on this type of fallacy: since it cannot be proven that there is no invisible entity made up of spaghetti and meatballs that is also the creator of the world and its inhabitants, it must be real.

1.2. Fallacy ad verecundiam

The ad verecundiam fallacy, or authority fallacy, links the veracity of a proposition to the authority of the person defending it, as if that provided an absolute guarantee .

For example, it is common to argue that Sigmund Freud’s theories about mental processes are valid because their author was a neurologist.

1.3. Argument ad consequentiam

This type of fallacy tries to show that the validity or not of an idea depends on whether what can be inferred from it is desirable or undesirable .

For example, an ad consequentiam argument would be to assume that the chances that the army will carry out a coup in a country are very low because the opposite scenario would be a severe blow to citizens.

1.4. Hasty generalization

This fallacy is a generalization not supported by sufficient data .

The classic example is found in the stereotypes about the inhabitants of certain countries, which can lead to fallacious thinking, for example, that if someone is Scottish, they must be characterized by their stinginess.

1.5. Straw man fallacy

In this fallacy, the opponent’s ideas are not criticized, but rather a caricatured and manipulated image of them .

An example would be found in a line of argument in which a political group is criticized for being nationalist, characterizing it as something very close to what was Hitler’s party.

1.6. Post hoc ergo propter hoc

It is a type of fallacy in which it is taken for granted that if one phenomenon occurs after another, it is caused by it, in the absence of more evidence to indicate that this is the case .

For example, one could try to argue that the sudden rise in the price of an organization’s shares has occurred because the start of the big game season has already arrived in Badajoz.

1.7. Ad hominem fallacy

By means of this fallacy, the veracity of certain ideas or conclusions is denied by highlighting the negative characteristics (more or less distorted and exaggerated) of the person who defends them, instead of criticizing the idea itself or the reasoning that has led to it.

An example of this fallacy would be found in a case in which someone despises the ideas of a thinker arguing that he does not take care of his personal image.

However, one must know how to distinguish this type of fallacy from legitimate arguments referring to the characteristics of a specific person. For example, appealing to the lack of university studies of a person who speaks about advanced concepts of quantum physics can be considered a valid argument, since the information given is related to the topic of the dialogue.

  1. Formal fallacies

Formal fallacies are not because the content of the premise does not allow the conclusion to be reached, but because the relationship between the premises makes the inference invalid .

That is why their failures do not depend on the content, but on the way in which the premises are linked, and they are not false because we have introduced irrelevant and unnecessary ideas into our reasoning, but because there is no coherence in the arguments we use.

The formal fallacy can be detected by substituting symbols for all the elements of the premises and seeing if the reasoning conforms to the logical rules.

2.1. Denial of the antecedent

This type of fallacy starts from a conditional of the type “if I give you a gift, it will be my friend” , and when the first element is denied, it is incorrectly inferred that the second is also denied: “if I do not give you a gift, it will not be my friend”.

2.2. Affirmation of the consequent

In this type of fallacy, we also start from a conditional, but in this case the second element is affirmed and it is incorrectly inferred that the antecedent is true:

“If I pass, I uncork the champagne.”

“I uncork the champagne, so I approve.”


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