Definition
Explanatory power is how much a theory explains. A theory with high explanatory power accounts for a wide range of observations, makes specific predictions, and rules things out — it tells you what should not happen as clearly as what should.
A weak explanation is one that can be stretched to fit any outcome. If a claim is compatible with every possible result, it explains nothing, because it forbids nothing. Real explanatory power comes from a theory taking risks: committing to predictions that could fail.
Why it matters
How it works
To judge explanatory power, ask what a theory predicts and what it forbids. A strong theory says clearly: if I am right, you will see this and not that. You then look for the forbidden cases. Survival of such tests builds confidence; a single clear failure counts heavily against the theory.
The best explanations combine wide reach with sharp predictions — and pair that power with parsimony, so the reach is not bought with endless assumptions.