Topic 3.2 Flawed Lines of Reasoning: identify and explain flaws in a line of reasoning, including common logical fallacies, and avoid them in your own writing.

What this topic is asking

Topic 3.2 (skill REO-1.A) asks you to find the flaws in a line of reasoning and to avoid them in your own writing. A line of reasoning can look orderly and still be broken if a step does not follow from the one before. The named logical fallacies are the recurring patterns of broken inference. The exam tests both halves: spotting a flaw in a passage and writing arguments free of them.

What makes reasoning flawed

The key idea is that truth and validity are different. A writer can state true facts and still reason badly if the link between the facts and the conclusion is broken. Reasoning is about the connection, and a fallacy is a broken connection that often sounds persuasive.

The common fallacies

• Hasty generalization. Drawing a broad conclusion from too few cases ("two of my friends failed, so the test is unfair to everyone").
• False cause (post hoc). Assuming that because one event followed another, the first caused the second ("sales rose after the ad, so the ad caused it" - ignoring other factors).
• Straw man. Misrepresenting an opponent's view as weaker or more extreme, then attacking that distortion instead of the real position.
• False dilemma. Presenting only two options when others exist ("either we ban phones or grades will collapse").
• Ad hominem. Attacking the person making an argument rather than the argument itself.
• Slippery slope. Claiming one small step must trigger an unstoppable chain to a disastrous end, without justifying each link.

Spotting flaws in a passage

When a multiple choice question asks why an argument is weak, locate the inference, not the topic. Ask: does the conclusion actually follow from what was offered? Then match the gap to its name.

Why this matters for the exam

Flawed reasoning appears on the multiple choice section (questions ask why an argument is weak or what assumption it depends on) and on the argument and synthesis essays, where your own reasoning must be sound to earn the upper half of the rubric. The sophistication point often rewards a writer who anticipates and avoids the obvious counter, which is exactly the discipline of avoiding fallacies.

Try this

Q1. Name three common logical fallacies and define one in a sentence. [Recall]

• Cue. For example hasty generalization (a broad conclusion from too little evidence), false cause, and straw man. Hasty generalization: drawing a sweeping claim from a sample too small to support it.

Q2. A writer argues that a new policy is wrong because the politician who proposed it once lied about an unrelated matter. Name the flaw and explain why the inference fails. [Short explanation]

• Cue. This is an ad hominem: it attacks the proposer's character rather than the policy. The inference fails because a person's past dishonesty about one thing does not show that this particular policy is wrong; the argument must be judged on its own reasoning and evidence.