The value of evidence lies in its ability to distinguish between competing explanations.
Evidence does not become informative simply because it agrees with an explanation.
The critical question is whether that same evidence could also be explained by competing theories.
If several explanations are equally consistent with an observation, the observation does little to distinguish between them.
The most valuable evidence is evidence that helps us discriminate between competing explanations.
The Principle
Philosopher Karl Popper introduced the concept of a crucial experiment: a test designed to distinguish between competing theories by potentially refuting at least one of them.
Physicist David Deutsch developed this further in The Logic of Experimental Tests (2016).
He explains that a crucial test requires competing explanations of the same phenomenon. Ideally, its possible outcomes are such that each would create serious problems for all but one of those explanations.
This changes how we should think about evidence.
Rather than asking whether an observation confirms our preferred explanation, we ask:
What competing explanations did the test discriminate between, and why does the result favor one over the others?
Why This Matters
This principle extends far beyond scientific experiments.
Whenever we evaluate a business strategy, an investment thesis, a policy, or an explanation of human behavior, multiple explanations may account for the same observations.
The challenge is not merely to find supporting evidence. It is to identify evidence that distinguishes between these competing accounts of reality.
A hundred observations that all competing explanations can accommodate may contribute less to our understanding than one observation that reveals a decisive difference between them.
The quantity of evidence matters less than its ability to resolve uncertainty between explanations.
This also explains why collecting more data does not necessarily produce better understanding. If the additional data cannot distinguish between competing explanations, the underlying problem remains unresolved.
The Practical Principle
When examining an important claim:
- Identify the competing explanations. What other accounts could explain the same observations?
- Determine where they disagree. What would we expect to observe if one explanation were correct rather than another?
- Find discriminating evidence. Seek observations or tests that expose those differences.
- Evaluate the result. Which explanations become problematic, and which better account for the evidence?
A crucial test does not guarantee certainty. Experimental assumptions may be wrong, and better explanations may remain undiscovered.
But it provides a more rigorous way to direct our inquiry.
The purpose of a good test is not to accumulate evidence for an explanation. It is to help us determine which explanation better accounts for reality.
References
- Popper, K. R. (1959). The Logic of Scientific Discovery. Hutchinson. Chapter 10, “Corroboration, or How a Theory Stands Up to Tests.”
- Deutsch, D. (2016). The Logic of Experimental Tests, Particularly of Everettian Quantum Theory. Studies in History and Philosophy of Modern Physics, 55, 24–33.
- Deutsch, D. (2011). The Beginning of Infinity: Explanations That Transform the World. Allen Lane.