Analogical Arguments: Persuading by Comparison

The Structure of Analogical Arguments

An analogical argument has this structure: Situation A has properties X, Y, and Z. Situation B also has properties X and Y. Therefore, Situation B probably also has property Z. The strength of the analogy depends on how relevant the shared properties are to the conclusion.

For example: 'The drug war in America has failed to reduce drug use despite massive enforcement spending. Similarly, prohibition of alcohol in the 1920s failed to reduce alcohol consumption. Therefore, prohibition-based approaches to substance control are likely to fail.' The analogy works because both situations share relevant features: prohibition of a desired substance, enforcement challenges, and entrenched demand.

Analogies are not deductive arguments -- they do not guarantee their conclusions. They are inductive, providing probabilistic support. The strength of the support depends on the relevance of the similarities and the significance of the differences between the compared situations.

What Makes a Strong Analogy

The key to a strong analogy is the relevance of the shared properties. Two situations can be similar in many ways but dissimilar in the ways that matter for the conclusion. A car and a horse can both transport people, but an argument about fuel efficiency would not transfer from one to the other because the relevant mechanisms are different.

A strong analogy shares properties that are causally connected to the conclusion. If you argue that a policy that worked in Sweden will work in the United States, the shared features must include the factors that made the policy effective in Sweden. If those success factors are absent in the United States, the analogy fails.

The fewer relevant differences between the compared situations, the stronger the analogy. If two situations are identical in all relevant respects, the analogy approaches certainty. In practice, there are always some differences, and the debate often centers on whether those differences are significant enough to undermine the analogy.

Attacking and Defending Analogies

To attack an analogy, identify relevant differences between the compared situations that would affect the conclusion. 'The comparison between Prohibition and the drug war fails because alcohol was widely used and culturally accepted before Prohibition, whereas most illegal drugs were never mainstream.' Whether this difference actually undermines the analogy is debatable, but it forces the proponent to address the disanalogy.

To defend an analogy, argue that the shared features are more relevant to the conclusion than the differences. You can also strengthen your analogy by providing multiple analogies that converge on the same conclusion, making it less likely that any one disanalogy is decisive.

The most effective use of analogy in debate is to make complex or abstract ideas concrete and accessible. Abstract policy arguments about 'externalities' and 'market failures' become vivid and understandable when compared to familiar situations.

• •Analogical arguments transfer conclusions from one situation to a relevantly similar one.
• •Strength depends on the relevance of shared properties to the conclusion.
• •Attack analogies by identifying relevant differences between the compared situations.
• •Defend analogies by showing shared features outweigh differences in importance.
• •Use multiple converging analogies to strengthen your case.