Definition
An analogy is a structural correspondence between two situations such that the roles played by elements in one map onto the roles played by elements in the other. The mapping is structural, not surface — "an atom is like a solar system" is an analogy because both involve a heavy center with lighter bodies orbiting around it, regardless of scale or material.
Why it matters
How it works
To make an analogy, identify the structural roles in the source situation and look for elements playing similar roles in the target. The mapping should be one-to-one (or carefully selective), preserve key relations, and project predictions from source to target that you can then test. Strong analogies generalize; weak ones depend on accidental surface similarities.