Why every part of an explanation must serve a purpose.
One of the most common mistakes in reasoning is introducing unnecessary assumptions, entities, or complications into our explanations of reality.
In The Fabric of Reality (1997), physicist David Deutsch offers his own formulation of Occam’s razor:
“Do not complicate explanations beyond necessity.”
His reasoning is straightforward: unnecessary complications introduce additional things that themselves require explanation, without necessarily improving our understanding.
Every component of an explanation should contribute something necessary to solving the problem it addresses.
If removing an assumption, entity, or mechanism does not reduce an explanation’s ability to account for the relevant phenomena, that component is superfluous.
This distinction matters because explanations can become increasingly complicated without becoming more accurate or informative.
When an explanation fails to account for an observation, we may attempt to preserve it by introducing additional assumptions, exceptions, or mechanisms. But unless these additions solve the underlying problem, they merely shift the difficulty elsewhere.
Simplicity Is Not the Objective
Deutsch makes an important distinction between explanations that are simple and explanations that contain no unnecessary complications.
The simplest explanation is not necessarily the best. Reality can be complex, and explaining it may require sophisticated theories involving entities and processes that are difficult to observe or understand.
The relevant question is not how many components an explanation contains, but whether those components are necessary.
Necessary complexity improves explanatory power. Unnecessary complexity adds problems without solving them.
In Chapter 4, “Criteria for Reality,” Deutsch takes this argument further. He proposes that when our best explanation requires an entity with complex and autonomous behavior, we have reason to regard that entity as real, even if we cannot observe it directly.
This connects the structure of our explanations with our understanding of what exists.
How to Apply the Principle
When evaluating an explanation, ask:
- What problem does this explanation solve? Identify exactly what needs explaining.
- What assumptions or entities does it introduce? Make every component explicit.
- What does each component explain? Determine its specific contribution.
- What happens if a component is removed? Does the explanation lose important explanatory power?
- Are additional assumptions concealing an unresolved problem? Challenge exceptions or modifications introduced merely to protect an existing belief.
The objective is not to simplify explanations at any cost. It is to eliminate components that contribute nothing necessary to our understanding.
An explanation should be no more complicated than the reality it needs to explain requires.
The fundamental principle is simple: keep what is necessary to explain reality, and challenge/reject everything that is not.
References
- Deutsch, D. (1997). The Fabric of Reality. Penguin. Chapter 4, “Criteria for Reality.”
- Deutsch, D. (2011). The Beginning of Infinity: Explanations That Transform the World. Allen Lane. Chapter 1, “The Reach of Explanations.”
- Mossé, B. (2025). How We Know What’s Real: Deutsch’s Criterion for Reality. Read article.