Week 15 — Logical Fallacies

Week of 2026-12-14 · Download .docx

Objectives

Identify and name at least eight logical fallacies in original examples and explain specifically why each is a fallacy
Revise a fallacious argument to make the same essential point without the fallacy
Distinguish the argument from the fallacy — explain why a flawed argument can lead to a true conclusion and why the flaw still matters

Key terms

Ad hominem: Attacking the person making an argument rather than the argument itself.
Straw man: Misrepresenting an opposing position in a weakened form, then defeating the weaker version.
False dichotomy: Presenting only two options when more options exist, eliminating legitimate alternatives.
Slippery slope: Claiming that one step inevitably leads to extreme consequences without evidence for each step in the chain.
Post hoc: Assuming causation from sequence — because B followed A, A must have caused B — when correlation is not causation.
Hasty generalization: Drawing a broad conclusion from an insufficient or unrepresentative sample.
Circular reasoning: Restating the claim as its own evidence — the conclusion appears embedded in the premise.
Red herring: Introducing an irrelevant issue to distract attention from the actual argument.

The concept

Logical Fallacies: When Reasoning Fails

A logical fallacy is a flaw in reasoning that makes an argument invalid — even if the conclusion it reaches happens to be true. This distinction matters: a fallacious argument is not automatically a false conclusion. A writer who argues 'You should take your vitamins because my neighbor got sick after stopping' is using post hoc reasoning — correlation, not causation — but vitamins may still be beneficial. The fallacy is in the reasoning, not necessarily in the claim. This is why learning to identify fallacies is not about dismissing claims but about demanding better support for them.

Twelve Fallacies in Practice

Ad hominem attacks the person, not the argument — disqualifying a climate scientist's data because of their personal politics leaves the data unaddressed. Straw man defeats a distorted version of the opponent's position — arguing against what the opponent did not say is easier, but it is not honest engagement. False dichotomy eliminates the middle ground — 'either support this policy or you want children to fail' pretends that only two positions exist in a complex debate. Slippery slope treats a first step as inevitably producing an extreme outcome — without providing evidence for each step in the chain, the slippery slope is a scare tactic, not a logical consequence. Post hoc confuses sequence with causation — A came before B, therefore A caused B. Hasty generalization projects a small sample's characteristics onto a large population.

Appeal to authority is fallacious when the authority cited is outside their field of expertise — a famous actor endorsing a financial product is not a financial expert, regardless of their fame. Bandwagon appeal argues popularity is proof — but what 'everyone believes' has been wrong throughout history. Circular reasoning embeds the conclusion in the premise — 'This law is fair because it treats everyone fairly' restates the claim without supporting it. Red herring distracts with an irrelevant issue. Appeal to nature assumes 'natural' means 'good' — arsenic and cholera are natural; many beneficial medicines are synthetic.

Steelmanning vs. Straw Man

The opposite of straw man is steelmanning: representing the strongest version of the opposing argument before addressing it. Steelmanning is more honest and more persuasive — an opponent whose best argument you can still defeat is a more impressive achievement than one whose weakest version you have dismantled.

Worked examples

Example 1: Example 1 — Identifying and naming: A student argues: 'We should not ban plastic straws. If we ban straws, next they will ban plastic bags, then all plastic packaging, and eventually all manufactured goods. This will destroy the economy.' The fallacy is slippery slope: no evidence is provided that each step in the chain will necessarily follow from the one before. The argument treats a single regulatory measure as an inevitable path to an extreme outcome.

Example 2: Example 2 — Patching a fallacy: Original (post hoc): 'The school installed a new counseling program in September. By December, the suspension rate had dropped 18 percent. The counseling program caused the drop.' The post hoc error: other changes may have occurred simultaneously. Patched version: 'The school installed a new counseling program in September. By December, the suspension rate had dropped 18 percent. A controlled comparison with three demographically similar schools that made no program changes in the same period showed an average drop of 2 percent, suggesting the counseling program is a likely contributor to the improvement.' The patch adds comparative evidence that rules out coincidence.

Common mistakes

Assuming that identifying a fallacy defeats the argument — it defeats the reasoning, not necessarily the conclusion. The correct response to a fallacious argument is to demand better support for the conclusion, not to assume the conclusion is false.
Confusing appeal to authority with ethos — citing a genuine expert in their actual field of expertise is ethos, not a fallacy. The fallacy occurs when the authority is cited outside their expertise, or when expertise is used to replace rather than support the argument.
Treating all emotional appeals as fallacious — a pathos appeal that accurately represents a real situation and connects it legitimately to the argument is valid rhetoric. The fallacy version of a pathos appeal manipulates emotion to distract from weak reasoning, not to illuminate real stakes.

Self-check

Try each one before you look. A miss here costs nothing and tells you exactly what to reread.

1. A writer argues: 'My opponent says we should reduce the school day by 30 minutes. Clearly, they think students should stop learning altogether.' This is an example of:

2. Post hoc ergo propter hoc is a fallacy because:

3. Circular reasoning (begging the question) is best identified by which characteristic?

4. A hasty generalization differs from a valid inductive inference primarily in that:

5. Steelmanning an opposing argument means:

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