Core 201 – Formal and Informal Fallacies

Formal and Informal Fallacies


This section of the Handbook introduces the concept of formal and informal fallacies while reviewing ethos, logos, and pathos. Specifically, we will address the following questions.

  1. What are fallacies?
  2. What is a formal fallacy?
  3. Why is it important to recognize formal fallacies?
  4. What is an informal fallacy?
  5. How can ethos, logos, and pathos be used to test an argument for fallacies?
  6. How do fallacies weaken arguments?
  7. Where can I find more information about generalizations, fallacies, analogies, and syllogisms?

1. What are fallacies?

Fallacies are errors or tricks of reasoning. We call a fallacy an error of reasoning if it occurs accidentally; we call it a trick of reasoning if a speaker or writer uses it in order to deceive or manipulate his audience. Fallacies can be either formal or informal.

Whether a fallacy is an error or a trick, whether it is formal or informal, its use undercuts the validity and soundness of any argument. At the same time, fallacious reasoning can damage the credibility of the speaker/writer and improperly manipulate the emotions of the audience/reader.

2. What is a formal fallacy?

Most formal fallacies are errors of logic: the conclusion doesn’t really “follow from” (is not supported by) the premises. Either the premises are untrue or the argument is invalid. Below is an example of an invalid deductive argument.

Premise: All black bears are omnivores.
Premise: All raccoons are omnivores.
Conclusion: All raccoons are black bears.

Bears are a subset of omnivores. Raccoons also are a subset of omnivores. But these two subsets do not overlap, and that fact makes the conclusion illogical. The argument is invalid—that is, the relationship between the premises doesn’t support the conclusion.

3. Why is it important to recognize formal fallacies?

“Raccoons are black bears” is instantaneously recognizable as fallacious and may seem too silly to be worth bothering about. However, that and other forms of poor logic play out on a daily basis, and they have real world consequences. Below is an example of a fallacious argument:

Premise: All Arabs are Muslims.
Premise: All Iranians are Muslims.
Conclusion: All Iranians are Arabs.

This argument fails on two levels. First, the premises are untrue because although many Arabs and Iranians are Muslim, not all are. Second, the two ethnic groups are sets that do not overlap; nevertheless, the two groups are confounded because they (largely) share one quality in common. One only has to look at comments on the web to realize that the confusion is widespread and that it influences attitudes and opinions about U.S. foreign policy.

4. What is an informal fallacy?

Informal fallacies take many forms and are widespread in everyday discourse. Very often they involve bringing irrelevant information into an argument or they are based on assumptions that, when examined, prove to be incorrect. Formal fallacies are created when the relationship between premises and conclusion does not hold up or when premises are unsound; informal fallacies are more dependent on the misuse of language and of evidence.

It is easy to find fairly well-accepted lists of informal fallacies, but that does not mean that it is always easy to spot them. Some moves are always fallacious; others represent ways of thinking that are sometimes valid and reasonable but which can also be misused is ways that make them fallacies.

5. How can ethos, logos, and pathos be used to test an argument for fallacies?

One way to go about evaluating an argument for fallacies is to return to the concept of the three fundamental appeals: ethos, logos, and pathos.

The concepts of ethos, logos, and pathos were first introduced in CORE 101 under the Approaches to Written Argument assignment. It may help you if you take some time to review the answers to the following questions before you move on:

  • What is logos?
  • How do I recognize and evaluate logos in an argument?
  • What is ethos?
  • How do I recognize and evaluate ethos in an argument?
  • What is pathos?
  • How do I recognize and evaluate pathos in an argument?
  • What is the rhetorical triangle?
  • How are logos, ethos, and pathos related to the rhetorical triangle?
  • What is kairos?
  • How do I recognize and evaluate kairos in an argument?
  • How can logos, ethos, pathos, and kairos work together?

Once you have refreshed your memory of the basics, you may begin to understand how ethos, logos, and pathos can be used appropriately to strengthen your argument or inappropriately to manipulate an audience through the use of fallacies. Classifying fallacies as fallacies of ethos, logos, or pathos will help you both to understand their nature and to recognize them when you encounter them. Please keep in mind, however, that the list of fallacies presented in the next section is by no means exhaustive and that some fallacies may fit into multiple categories.

Fallacies of ethos relate to credibility. These fallacies may unfairly build up the credibility of the author (or his allies) or unfairly attack the credibility of the author’s opponent (or her allies). Some fallacies give an unfair advantage to the claims of the speaker or writer or an unfair disadvantage to the opponent’s claims. These are fallacies of logos. Fallacies of pathos rely excessively upon emotional appeals, attaching positive associations to the author’s argument and negative ones to the opponent’s position.

6. How do fallacies weaken arguments?

Both formal and informal fallacies are errors of reasoning, and if a speaker or writer relies on such fallacies, even unintentionally, she undercuts her argument. For example, if someone defines a key term in her argument in an ambiguous, vague, or circular way, her argument will appear very weak to an astute audience.

In addition, when listeners or readers spot questionable reasoning or unfair attempts at audience manipulation, more than their evaluation of the author’s argument (logos) may be compromised. Their evaluation of the credibility of the speaker (ethos), and perhaps their ability to connect with that speaker on the level of shared values (pathos), also may be compromised. At the very least, the presence of fallacies will suggest to an audience that the speaker or writer lacks argumentative skill.

7. Where can I find more information about generalizations, fallacies, analogies, and syllogisms?

If your assignment requires you to go into greater depth, you will find additional information in the CORE 201 Appendix under these questions:

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