Hard to Vary
Updated 2026-08-05
INTRODUCTION
English translation pending.
CORE DEFINITION
A criterion of good explanation proposed by David Deutsch. A theory earns its status by being hard to vary: change one of its details and the explanation stops working, because the parts are tightly tied to the evidence they account for. Bad explanations, such as myth or unfalsifiable doctrine, are easy to vary, since any inconvenient fact can be absorbed by adjusting the story. The test is not how much a theory explains but how little room it leaves to manoeuvre. Hard-to-vary explanations are also the ones with genuine reach and predictive power.
SCAFFOLDING EFFECT
Reduce cognitive load
- Rigidity Test: perturb one detail and see whether the explanation survives intact. - Patch Audit: count how many ad hoc additions a theory needed to absorb new evidence. - Reach Check: prefer accounts whose parts cannot be swapped without breaking.
Anchor fast decisions
A good explanation constrains its own content, because each element is load-bearing for the evidence it accounts for. Changing a value or a mechanism therefore breaks the fit, which is exactly what makes it hard to vary. An explanation that can absorb anything is compatible with everything, and compatibility with every possible outcome carries no information. Easy variation is thus a symptom of low explanatory content rather than of flexibility.
MINIMUM ACTION
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Explanatory_powerverified
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