Questions: Analogical Arguments: Strength and Weakness

Question 1

The analogy 'the eye is like a camera' is used to support two conclusions: (1) that both form inverted images on a light-sensitive surface, and (2) that both can be repaired when damaged. How does the analogy's strength differ?

• A. The analogy is equally strong for both conclusions because the number of similarities is the same
• B. Strong for (1) because the shared optical properties directly explain image formation; weak for (2) because eyes heal biologically and cameras don't — a directly relevant difference
• C. Weak for both because eyes and cameras are too different at the molecular level
• D. Analogy strength cannot be evaluated without counting all shared properties

Answer: (B)

Analogy strength is conclusion-dependent. For image formation, the structural parallels (lens, inverted projection, light-sensitive surface) are causally relevant to how images form — the shared properties explain the target claim. For repair, there is a directly relevant difference: biological tissues heal through cellular regeneration while cameras have no such mechanism. A relevant difference in the domain of the conclusion undermines the analogy even when many other similarities exist.

Question 2

Which factor most directly weakens an analogical argument, even if the two things being compared share many properties?

• A. The objects come from different categories (e.g., biological vs. mechanical)
• B. There are more than ten observable differences between the objects
• C. A difference in a property that is directly relevant to the specific conclusion being drawn
• D. The analogy is based on a single source case rather than multiple cases

Answer: (C)

A relevant difference — one that specifically bears on the conclusion — is the most potent weakener of an analogy. Category differences (option A) and sheer number of differences (option B) don't automatically weaken an analogy if those differences don't connect to the conclusion. Option D (single source) is a real weakener but less decisive than a relevant difference. The question is always: does this difference matter for *this specific claim*?

Question 3

An analogical argument that draws on multiple independent source cases is generally stronger than one based on a single source case.

• T. True
• F. False

Answer: True

Sample diversity strengthens analogical arguments. If a pattern holds across varied, independent cases, it is less likely to be a fluke specific to one context. An argument that sleep improves athletic performance is stronger if it holds for basketball, football, swimming, and endurance sports than if it is based only on basketball data — the pattern's persistence across diverse cases provides inductive support that it is genuine rather than context-specific.

Question 4

The more properties two things share, the stronger any analogy between them, regardless of which conclusion is being drawn.

• T. True
• F. False

Answer: False

This is the central misconception about analogical reasoning. Shared properties strengthen an analogy only when they are relevant to the specific conclusion. Irrelevant similarities — however numerous — do not strengthen the argument. A human and a rock share many properties (both are material, both exist in time, both have mass), but this does nothing to support conclusions about cognition. Relevance is what matters, not the raw count of shared features.

Question 5

Why must you specify the conclusion before you can judge whether an analogy is strong or weak?

Model answer: Analogy strength is not a fixed property of the analogy itself — it is relative to the conclusion being drawn. The same shared properties may be highly relevant to one conclusion and irrelevant to another. To evaluate whether the similarities outweigh the differences, you need to know which similarities and differences are relevant — and relevance is defined by the conclusion. Without knowing what claim the analogy is supposed to support, you cannot determine which shared features count toward or against it.

The 'eye is like a camera' analogy is excellent for optics pedagogy and poor for biomedical repair reasoning — the same analogy, evaluated against different conclusions, has different strength. Evaluating an analogy always requires first asking: for *this conclusion*, do the relevant similarities between these cases outweigh the relevant differences? That question cannot be answered until the conclusion is specified.