The art of thinking · First principles thinking and its adaptations
Reasoning by analogy
Also known as: Analogical reasoning, Argument from analogy
German: Analogieschluss
In logic and problem solving, reasoning by analogy draws a conclusion about one case from its similarity to another, known case — for example, designing or documenting a new product the way comparable products have been designed or documented.
- Thinking models
- Philosophy
- Problem solving
In one sentence
Reasoning by analogy concludes from a known, similar case to a new one — efficient, but it inherits the assumptions of the case it copies.
Example
The manual of a new filler is built by copying the manual of the previous model. That works for the unchanged stations, but the new setup mode with reduced speed is missing because the old machine had none.
Explained in context
Context cards connect this term with others to answer one question. Also in British English and German.
How it applies
- Everyday reasoning: Most decisions are made by analogy — "this is like the last project, so we do what worked then". It is fast and usually adequate.
- The contrast: In his 2012 Q&A with Wired, Elon Musk said that physics teaches you to reason from first principles rather than by analogy. Since then the pair has been the standard way of explaining first principles thinking.
- Technical documentation: Reusing the structure of a legacy manual or of the previous product's manual is reasoning by analogy. It is sound where the products really are alike and risky where operating modes, hazards or audiences differ, because the copy carries over assumptions nobody checks.
Reasoning by analogy vs. first principles thinking
The two are not opposites in practice. Analogies supply hypotheses and save effort; first principles thinking checks whether the analogy's assumptions still hold for the case at hand. The risk lies in an analogy that is never questioned.
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