Analogical Reasoning

Arguments by analogy are among the most common forms of reasoning in everyday debate and in LNAT passages. When an author argues that because something is true in one case, it should also be true in a similar case, they are using analogical reasoning. The LNAT tests your ability to evaluate whether such analogies are valid.

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What is an Argument by Analogy?

An argument by analogy has the following structure:

1. Situation A has characteristics X, Y, and Z
2. Situation B also has characteristics X and Y
3. Therefore, Situation B probably also has characteristic Z

The argument works by claiming that because two things are similar in known respects, they are likely similar in a further, unknown respect.

Simple Example

"Requiring cyclists to wear helmets has significantly reduced head injuries. Similarly, requiring motorcyclists to wear high-visibility jackets would significantly reduce motorcycle accidents."

The analogy compares cycling helmet laws to a proposed motorcycle high-visibility rule. Both involve mandatory safety equipment for two-wheeled road users. But does the analogy hold?

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Evaluating Analogies: Relevant Similarities and Differences