Unit 1: Logic
1.4 Fallacies – The Basics
A fallacy is a defect in an argument that involves mistaken reasoning; sometimes fallacies are committed purposefully, to influence or mislead the reader or listener.
- A formal fallacy is a defect that can be detected by examining the form of an argument.
- An informal fallacy is a defect that can be detected by examining the content of the argument.
Video
View just the first five minutes of this video to reinforce your understanding of the important distinction between formal and informal fallacies.
1.4.1 Formal Fallacies – Some Examples
Formal fallacies occur in arguments that use bad (invalid) form. The scope of this course does not permit extensive examination of a wide range of argument structures, or forms. So, there will not be extensive consideration of fallacies arising from defective form. We will, none-the-less, look briefly at two examples of formal fallacies; each results from invalid (defective!) use of an argument form that we visited earlier in our examination of the deductive argument types.
Example 1: Affirming the Consequent
This fallacy might be seen as a flawed (invalid!) attempt to use the modus ponens argument form. Recall that one of the premises in modus ponens affirms the antecedent of the hypothetical premise. In effect, with modus ponens, the antecedent necessitates the consequent. In the fallacious example below, however, the consequent is affirmed rather than the antecedent:
Premise 2: There is time to clean the kitchen.
Conclusion: Therefore, I neglected my homework.
Recall the correct form for modus ponens from section 1.3.1:
A
therefore C
Instead, the fallacious argument uses this invalid form, affirming the consequent (C) instead of the antecedent (A):
C
therefore A
This reasoning is defective. Making time to clean the kitchen could result from skipping a variety other activities besides homework. It is not necessary to make this time by neglecting the homework, though it could be sufficient.
Example 2: Denying the Antecedent
This fallacy can be seen as a defective (invalid!) use of the modus tollens argument form. Recall that one of the premises in modus tollens denies the consequent of the hypothetical premise. In the fallacious example below, however, the antecedent, is denied instead of the consequent:
Premise 2: Ozzie is not a sweepstakes winner.
Conclusion: Thus, Ozzie cannot buy a new EV.
The correct form for modus tollens from section 1.3.1 looks like this:
not C
therefore not A
Instead, the fallacious argument used this invalid form, denying the antecedent (A) instead of the consequent (C).
not A
therefore not C
The reasoning is defective. Ozzie may have other financial options, or prices might come down. Winning the lottery is not a necessary requirement for Ozzie to get the electric vehicle. (But if he did win, it would help!)
1.4.2 Informal Fallacies
An informal fallacy is one that can be detected by examining the content of the argument rather than the form. While informal fallacies can sometimes be attributed to hasty or negligent reasoning, more often they are committed with the clear intent to mislead the listener or audience, to justify belief in a claim that is not true. Further, these fallacies may arise in an atmosphere charged with emotion.
Informal fallacies are attributed not just to arguments with actual premise-conclusion form, but also to wider use of language that is intended to establish a claim or make a point.
There are many accounts (lists, enumerations) of informal fallacies, not only in logic texts but in materials from other disciplines concerned with communication. A particular fallacy may be identified with different names in different lists of fallacies. For example, the “Black and White” fallacy in the list of common informal fallacies in our linked course reading is referred to in other lists as “false choice” or “false dilemma” or “false dichotomy.” Whatever it is called, this fallacy commits the same error by presenting only two alternatives, as if no other options are possible.
When reviewing the following material on informal fallacies, watch for some that correspond to defective use of argument types (inductive ones especially) that we considered in the section on “Argument Types.” A fallacious claim may commit more than one fallacy; for example, some fallacious statements commit the fallacy known as “appeal to emotion” in addition to another fallacy.
Reading
Read this presentation on common informal fallacies. [CC-BY-NC-ND]
The fallacies presented in the linked reading assignment are summarized in this quick-reference table.
Summary of Fallacies from Assigned Reading
| Fallacy Name | Brief Description | Example |
|---|---|---|
| Accident, aka sweeping or hasty generalization | A general conclusion is drawn from a non-representative sample. | I met no one I liked first week on this dating site. The site is useless! |
| Argument against the person, aka genetic fallacy, argument ad hominem | Arguer committing the fallacy attacks the opponent personally (and possibly abusively), instead of addressing the argument itself. | I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent’s youth and inexperience.(Ronald Reagan) |
| Ambiguity, aka equivocation | A term or phrase is used or can be interpreted in two different senses. | Pete says his dog loves children. You better not bring your kids to his party – they may be eaten! |
| Appeal to authority | A claim is made by an unqualified authority who lacks expertise on the topic. | My grandmother says the monsoon will be weak this year – she saw some signs. |
| Appeal to emotion | Highly emotive language is employed to illicit a visceral response. | You better join the neighborhood watch. Just imagine the damage to your property and assaults on your family that will occur if you do not join now! |
| Appeal to ignorance | The premises provide no support for the conclusion/claim. Often involves a claim incapable of being proved. | The claims of astrology have never been proven to be true so they must be false. |
| Appeal to pity | The arguer makes his claim/point by inspiring the reader/listener to feel pity. | The overtime hours should be given to Bob. He has six kids to feed and his wife has incurred large medical bills. |
| Begging the question | The arguer makes inadequate premises seem adequate by omitting a key information, or by restating the conclusion as a premise, or by arguing in a circle. | To be an advocate of revolution, you need a vision for the future because a vision for the future is required for being an advocate of revolution. |
| Black or white fallacy, aka false dichotomy, false dilemma | A disjunctive either-or premise presents two alternatives as if there are no other choices. | Either we have medicare-for-all or we have private insurance. Those are our options. |
| Composition | A characteristic is erroneously transferred from the parts to the whole. | This chair is made of particles that are in motion. So the chair is in motion too. |
| Division | Attributes of the whole are erroneously transferred to its parts. | My new car was made in the USA, so all of its parts were made here too. |
| False cause | The connection between the premise and the conclusion involves a causal connection that does not exists or is insignificant. | Joe had a massive heart attack right after eating two whopper burgers for lunch. Those burgers are killers! |
| Red herring | The listener is lead off the track of the argument. | Video streaming on computers can be a major distraction from getting school work done. But some of those videos are so cool it would be terrible to miss them! |
| Slippery slope | A claim/conclusion based on an unlikely chain of events is presented as if it is inevitable. | This week we are taking down statues of confederate general Robert E. Lee. Next it will be George Washington, then Thomas Jefferson. It will never stop! |
| Strawman | The argument is distorted, with the arguer claiming to win the original argument when it is the related/distorted argument being addressed. | An argument for immigration reform is recast as and then put down as an argument for open borders. Or, an argument for controls on acquisition of firearms is recast and then addressed as an argument to abolish the 2nd amendment. |
| False (or weak) analogy | Argument is based on a similarity between two things that is not strong enough to support the conclusion. | Running a country is like running a business, so a businessperson should be elected. |
This table summarizes fallacies covered in Informal Fallaciesfrom Module 8 of the Lumen Principles of Public Speaking[CC-BY-NC-ND]. Alternate names are noted for some fallacies. |
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Check Your Understanding
Apply Your Understanding
Learning to recognize informal fallacies when you hear them in everyday discourse can be an enriching takeaway from this unit. Consider what you read and/or hear on news media, social platforms, or wherever you spend time paying attentions to what others are saying and writing. Look/listen for arguments or language that make claims that seem misleading. Take note and check against the Summary of Fallacies table above. You may be surprised at the prevalence of fallacious claims being made.
