The power of an explanation lies in what it rules out.
Every explanation makes a claim about how reality works. But the strength of that claim depends on something we rarely consider: what the explanation says cannot happen.
Karl Popper recognized this in Conjectures and Refutations (1963):
“Every ‘good’ scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.”
This is a profound insight into the nature of knowledge.
An explanation that is compatible with every possible outcome tells us almost nothing. It places no constraints on reality. Whatever happens, the explanation remains intact.
A more precise explanation is different. It excludes possibilities. It makes claims about what must follow, what cannot occur, and which outcomes would be inconsistent with our understanding.
The more possibilities an explanation rules out, the more information it potentially gives us about reality.
But there is a price for this precision: the explanation becomes more vulnerable to being wrong.
That vulnerability is not a weakness. It is what makes the explanation informative and testable.
Why This Matters
The principle reaches far beyond scientific theories.
Our decisions depend on explanations of how the world works. Whether we are evaluating a business, developing a strategy, interpreting events, or assessing someone’s judgment, we rely on assumptions about what is possible, probable, and impossible.
The usefulness of those assumptions depends partly on what they exclude.
A strategy that accommodates every possible outcome provides little guidance. A forecast that can be interpreted as correct regardless of what happens offers little predictive value. An explanation that retrospectively accounts for every success and failure gives us no reliable way to distinguish between them.
Good explanations constrain our expectations. Bad explanations accommodate them.
This is why precision matters. A vague explanation may appear sophisticated or comprehensive, but unless it rules something out, it contributes little to our ability to distinguish between competing accounts of reality.
The Practical Principle
When evaluating an explanation, ask:
- What does this explanation rule out? Identify the possibilities it excludes.
- What must be true if the explanation is correct? Understand its necessary implications.
- What distinguishes it from competing explanations? Determine what one explains or predicts that another does not.
- Are its restrictions supported by sound reasoning? Arbitrary prohibitions are not evidence of understanding.
- Has it survived serious attempts to challenge it? An informative explanation must also withstand criticism and testing.
There is an essential qualification: a theory is not true merely because it makes bold claims. A false theory can also rule out many possibilities. The value comes from combining explanatory precision with successful criticism and testing.
The broader lesson is that knowledge is not measured by how much an explanation can accommodate, but by how effectively it distinguishes what is possible from what is not.
An explanation becomes useful when it rules things out. It becomes reliable when those restrictions withstand contact with reality.
References
- Popper, K. R. (1963). Conjectures and Refutations: The Growth of Scientific Knowledge. Chapter 1, “Science: Conjectures and Refutations.”
- Popper, K. R. (1959). The Logic of Scientific Discovery.
- Deutsch, D. (2011). The Beginning of Infinity. Chapter 1, “The Reach of Explanations.”