Strevens on Explanatory Depth

The Core Idea

Michael Strevens argues that good scientific explanations don’t just cite causes. They cite the difference-making causes while abstracting away irrelevant details.

The Kairetic Account

Strevens’ “kairetic” account (from the Greek word for “decisive moment”) says:

An explanation should include:

  • All and only the difference-makers
  • The causal factors that make a difference to the outcome
  • Abstracted to the right level of generality

Why This Matters

Against Simple Causation

Not all causes belong in explanations. The presence of oxygen is causally necessary for a fire, but we don’t cite it when explaining why a particular fire started, unless oxygen levels were the difference-maker.

Against Pure Laws

Laws alone don’t explain. “Objects fall at 9.8 m/s²” doesn’t explain why this particular object fell. We need initial conditions and to show why they mattered.

The Right Level of Abstraction

Good explanations abstract away details that don’t make a difference. We explain genetic inheritance without citing quantum mechanics, not because QM is wrong, but because it’s not difference-making at that level.

Application to Research

This framework helps evaluate explanations:

  • Am I citing all the difference-makers?
  • Am I including irrelevant causal factors?
  • Am I at the right level of abstraction for my explanatory target?

Tensions and Questions

  • How do we identify difference-makers before we have a full causal model?
  • Does this work for statistical explanations?
  • What about historical explanations where everything matters?

Connection to My Work

Strevens’ framework shapes how I think about:

  • Building computational models (what to include?)
  • Writing up results (what level of mechanism to cite?)
  • Evaluating theories (are they at the right grain?)

Key Sources

  • Strevens, M. (2008). Depth: An Account of Scientific Explanation
  • Strevens, M. (2004). “The Causal and Unification Approaches to Explanation Unified—Causally”