Informal Fallacies

An informal fallacy is a reasoning error that arises not from flawed logical structure but from problems in content, context, or language. Informal fallacies often appear persuasive and seem like good arguments — they fail because of what is being said, not merely how it’s structured. They typically occur in real dialogues and pose a serious obstacle to reaching truth.

How It Appears Per Course

PHIL 252

Introduced in Unit 6 as the informal counterpart to the formal fallacies (Affirming the Consequent, Denying the Antecedent) introduced in Unit 3. While formal fallacies violate logical structure, informal fallacies corrupt the content, context, or language of the argument.

Walton’s Five Conditions for a Fallacy

For something to count as a fallacy (rather than just a bad argument), it must:

1. Be an argument (or at least look like one)
2. Fall short of some standard of correctness
3. Be used in a real context of dialogue
4. Have a semblance of correctness — it must look plausible enough to deceive
5. Pose a serious problem to achieving the goal of the dialogue

Formal vs. Informal Fallacies

	Formal Fallacy	Informal Fallacy
Error type	Invalid logical structure	Content, context, or language
Examples	Affirming the Consequent, Denying the Antecedent	Equivocation, Amphiboly, Composition, Division
Can be detected by	Truth-value mapping / form alone	Analysis of meaning, context, assumptions

The Six Fallacies of Ambiguity (Unit 6 Focus)

These are all covered in detail in FallaciesOfAmbiguity:

1. Equivocation
2. Amphiboly
3. Accent
4. Composition
5. Division
6. Hypostatization

Fallacies of Distorting the Facts (Unit 7 Focus)

These are all covered in detail in FalseCause:

1. False Analogy
2. Post Hoc Ergo Propter Hoc
3. Mere Correlation
4. Spurious Correlation
5. Data Dredging
6. Slippery Slope
7. Irrelevant Thesis (Red Herring)

Bias as a Source of Fallacy

Having preferences, attitudes, and interests is not itself a fallacy — bias becomes a problem when it leads to:

• Unfair reasoning (applying different standards to different groups)
• Inaccurate perception (seeing what we want to see)
• Inconsistent reasoning (special pleading)

See Bias.

Commitment to Truth

Informal fallacies matter because critical thinking only makes sense if truth is non-relative. If “all opinions are equally valid,” there is no point to identifying fallacies. The commitment to truth is the foundation that gives fallacy detection its purpose.

Cross-Course Connections

FallaciesOfAmbiguity — the specific fallacies of Unit 6
FalseCause — the False Cause family and other fallacies of distorting facts from Unit 7
Validity — formal fallacies covered in Unit 3
Argument — fallacies are failures of argument
Bias — bias enables and often drives informal fallacies
Bullshit — bullshit often works by exploiting informal fallacy patterns

Key Points for Exam/Study

• Informal fallacy ≠ simply a bad argument — it must look convincing (semblance of correctness)
• The error is in content/context/language, not in logical form
• Real dialogue context is key to Walton’s definition
• Truth-relativism is incompatible with critical thinking — fallacy detection requires a standard
• Emotions and interests don’t disqualify you from good reasoning, but they must be identified and corrected for

Open Questions

• How do we draw the line between a “bad argument” and a “fallacy”? Is the semblance of correctness a necessary condition or just a typical feature?