Recipe

Check a suspect argument for an informal fallacy

Use when: an argument feels wrong but its form looks fine, or you need to pin down what is wrong with it

Goal: the first of the four questions the argument fails, plus one sentence saying what its premises fail to do

Taught in What makes a fallacy

1. 1

   Write the premises and conclusion in standard form. Supply any missing premise charitably.

   Example

   "Don't use that budgeting app. The company that makes it also sells video games." Premise: the maker also sells video games. Conclusion: you shouldn't use the budgeting app.

   Why: you can't ask whether reasons support a conclusion until you know which sentences are which.

2. 2

   Ask whether the premises, if true, would bear on the conclusion at all.

   Example

   Selling video games says nothing about whether a budgeting app is good. The reason points at the company's other products, not the app. The check stops here.

   • they would not — a fallacy of relevance; say what the reasons point at instead.
   • they would — go on to the next question.

   Why: an irrelevant reason gives zero support however true it is, so nothing later can rescue it.

3. 3

   Ask whether the relevant premises give enough support. Look for tiny or lopsided samples and for causes the evidence doesn't reach. Hasty generalization (Chapter 6) and the causal fallacies (Chapter 7) fail here.

   Why: relevant evidence can still be far too thin to carry the conclusion.

4. 4

   Look for a premise that restates the conclusion, a framing that allows only two options, a question with a claim built in, or a rule applied to its exception. Chapter 6 names the common patterns that fail here.

   Why: an argument can't give you a reason to accept a claim it already takes for granted.

5. 5

   Look for a key word used in two senses, a sentence with two readings, or a word about the parts read as a word about the whole. Chapter 7 names the common patterns that fail here: equivocation, amphiboly, composition, and division.

   Why: if the premises are true only on one reading and the conclusion follows only on the other, nothing connects them.

6. 6

   Name the first question the argument fails and say, in one sentence, what the premises fail to do. If it passes all four, go on to the three questions from Chapter 3.

   Example

   "Fails at relevant: the maker's other products say nothing about whether this app is good."

   Why: the name of a pattern is a claim that still needs support; the one-sentence reason is that support.