Identify the fallacy in the following argument: “Alan is tall, dark and…

Concept: An argument from analogy claims that because two things are alike in several known respects, they are alike in one further respect as well. Such an inference is only as strong as the relevance of the shared respects to the respect concluded — the shared attributes must be causally or statistically connected to the attribute being inferred. When the cited similarities have no such bearing on the concluded attribute, the inference is a weak analogy, an informal fallacy of weak induction.

Application: Apply that test to the argument step by step.

1. Identify the form: two particular individuals, Alan and Bill, are compared, and a further attribute is transferred from one to the other. This is an analogical inference about a single further individual, not a claim about a whole class.

2. List the shared attributes offered as evidence: tall, dark and handsome.

3. Identify the attribute inferred from them: having blue eyes, that is, iris colour.

4. Test the relevance link: stature, complexion and attractiveness are neither causes of nor reliable statistical indicators of iris colour, so sharing them does not raise the probability that Bill has blue eyes.

5. Because the analogy rests on attributes irrelevant to the attribute concluded, the inference is a weak analogy.

Cross-check: Compare the argument against the structure each of the other named fallacies requires.

• Inconsistency requires claims that cannot all be true together; “Alan has blue eyes” and “Bill is tall, dark and handsome” stand together without contradiction.

• Slippery slope requires a chain running from a first step through further steps to an extreme outcome; the argument contains no such chain.

• Hasty generalization requires a general claim about a whole class drawn from too few or unrepresentative instances; the conclusion here is about one further individual, Bill, and no class-wide claim is made.

• Weak analogy requires a similarity-based inference whose shared attributes are irrelevant to the inferred attribute, which is exactly the structure above.

Result: The argument commits the fallacy of weak analogy (also called false analogy), an informal fallacy of weak induction.