Analyse how analogies and general principles are used to extend reasoning and when they succeed or fail.
An analogy argues: "Situation A is relevantly similar to Situation B. We treat Situation B in a certain way. Therefore, we should treat Situation A the same way." An analogy is only as strong as the relevant similarities between the two situations.
To evaluate an analogy: (1) identify what similarities are claimed, (2) assess whether those similarities are genuinely relevant, and (3) identify any disanalogies — relevant differences that undermine the comparison.
"Allowing people to eat unhealthy food is like allowing people to drink poison. We ban poison, so we should ban unhealthy food."
Analysis: Disanalogies: poison is immediately lethal while unhealthy food harms gradually; the quantities matter in food but not poison; people have greater personal choice in diet. These differences undermine the analogy.
"Testing new medicines on animals is similar to testing them on human volunteers: both involve potential harm for medical benefit. Since we allow human testing with informed consent, we should apply equally rigorous ethical oversight to animal testing."
Analysis: The relevant similarities (potential harm, medical benefit) are genuine. The analogy supports applying ethical oversight — a reasonable conclusion from the comparison.
When an argument uses a principle, test it by: (1) Is the principle widely acceptable? (2) Is it applied consistently? (3) Are there counter-examples that show the principle has limits?
Principles can be challenged by showing they lead to unacceptable conclusions in other cases ("reductio ad absurdum" style). If a principle implies something clearly wrong, the principle itself may be flawed.
Principle: "The government should never restrict personal freedoms." Application: "Therefore, the government should not require seatbelts."
Analysis: Challenge: most people accept that some freedom restrictions are justified to prevent harm to self or others. The absolute form of the principle leads to problematic applications — we might accept a modified principle: "The government should not restrict personal freedoms without good reason."
Evaluate the analogy used in this argument. Consider both its strengths and any disanalogies.
Answer in Practice →Evaluate whether the principle supports the conclusion. Are there challenges to how the principle is applied here?
Answer in Practice →