Questions: Analogical Reasoning and Argument by Analogy

Question 1

A critic of Judith Thomson's violinist analogy points out that conception (unlike waking up connected to a stranger) can involve a voluntary act. Under what condition does this disanalogy actually undermine Thomson's conclusion?

• A. Any difference between the cases automatically defeats the analogy, so the argument fails
• B. Only if the voluntary nature of conception is relevant to the moral conclusion about the permissibility of disconnecting from the violinist
• C. Only if the critic can identify three or more disanalogies, since a single difference is not enough
• D. It always undermines the analogy, because disanalogies reveal that the cases are fundamentally different

Answer: (B)

A disanalogy defeats an analogical argument only when it is *relevant to the conclusion*. Thomson's analogy argues that being kept alive by another person's body does not automatically obligate that person to continue. The critic's disanalogy — voluntary conception — is relevant only if voluntarily creating a dependency changes the moral obligation to sustain it. Whether this disanalogy is relevant is itself a substantive moral question, not a logical one. The analogy may survive if the critic cannot show that voluntariness changes the obligation in the relevant way.

Question 2

Which of the following analogical arguments is STRONGEST, given the criteria for evaluating analogical reasoning?

• A. Country A and Country B are both in the Northern Hemisphere, so they probably have similar economic policies
• B. Drug X cured the same disease in mice and rats, sharing 12 physiologically relevant biological pathways with humans, so it is likely to be effective in humans too
• C. City A and City B both have rivers, so they probably have similar flood risks
• D. Author A and Author B both wrote in the 19th century, so their novels probably share the same themes

Answer: (B)

Option B is strongest because it satisfies all key criteria: many similarities (12 pathways), those similarities are directly relevant to the conclusion (biological pathways determine drug efficacy), and the scope of the claim is appropriately narrow (likely effective). Options A, C, and D all rest on similarities (hemisphere, river, century) that are not clearly relevant to the proposed conclusions. Relevance of similarities — not mere quantity — is the decisive factor.

Question 3

Finding any difference between two cases being compared in an analogical argument defeats the analogy.

• T. True
• F. False

Answer: False

Disanalogies only undermine an analogical argument when they are *relevant to the conclusion*. Two cases will always differ in countless ways, most of which have nothing to do with what is being argued. A car and a bicycle differ in that one has an engine — but this difference is irrelevant to an analogy about road safety regulations based on speed limits. The systematic evaluation requires asking, for each difference: does this difference affect the property being argued about? If not, the disanalogy is harmless.

Question 4

Only similarities that are relevant to the conclusion strengthen an analogical argument.

• T. True
• F. False

Answer: True

This is the central principle of analogical evaluation. Two countries might share dozens of surface features — similar population sizes, similar climates, similar historical periods — but if none of those features are relevant to the economic conclusion being drawn, the analogy is weak despite the many similarities. Relevance is determined by causal or explanatory connection: does the shared property actually affect the property being predicted? Quantity of similarities is only evidence of strength when those similarities bear on the conclusion.

Question 5

Why is a disanalogy only an effective rebuttal if it is relevant to the conclusion? Explain using an example.

Model answer: A disanalogy is relevant when the difference between the cases affects the very property being inferred. If I argue that City A's traffic plan should work in City B because both have similar populations, road density, and commuter patterns, pointing out that the cities have different names is an irrelevant disanalogy — the difference doesn't affect traffic behavior. But pointing out that City A has flat terrain while City B is mountainous IS relevant if terrain affects how traffic flows. The same logical principle applies in moral philosophy: a disanalogy matters only if it plausibly changes whether the conclusion holds.

This principle explains why analogical arguments are often productive even when disanalogies exist. The debate over Thomson's violinist focuses not on whether differences exist (they obviously do) but on whether those differences are morally relevant — whether they change the obligation in question. This forces the discussion to identify exactly which features of a situation determine moral conclusions, which is far more illuminating than simply noting the cases differ.