Definition
Instrumentalism is the view that scientific theories are merely tools for predicting observations — they make no claims about what is really happening in the world. Deutsch argues this position is incoherent and actively harmful to scientific progress.
Why It Matters
If we treat theories as mere tools rather than explanations of reality, we lose the ability to know when they will fail. True progress comes from knowing why things happen, not just being able to predict the next number.
Core Concepts
- The instrumentalist claim: Theories are instruments for organizing and predicting experience, not descriptions of reality. ‘The electron exists’ means only ‘acting as if electrons exist yields accurate predictions.’
- Relation to positivism: Logical positivism held that only statements verifiable by observation are meaningful. Since unobservable entities can’t be directly verified, claims about them are ‘meaningless’ — only the predictive rules matter.
- Deutsch’s refutations:
- Prediction requires explanation: To apply a rule of thumb correctly, you must know the domain in which it holds — and that requires an explanation of why it holds. Pure predictive tools without explanation cannot be safely extrapolated.
- Rules of thumb break at edges: Without knowing the mechanism behind a predictive rule, you cannot know when it will fail. Good explanation tells you the limits of your predictions.
- Science has explanatory content: Quantum mechanics doesn’t just predict — it tells us (on Deutsch’s reading) that there are many parallel histories. Stripping this out leaves the mathematics without meaning.
- Instrumentalism collapses into denial of realism: If electrons are not real, what is doing the predicting? The mathematician’s symbols? Symbols without referents are not a scientific theory.
- Copenhagen interpretation: The dominant interpretation of quantum mechanics is instrumentalist — ‘shut up and calculate.’ Deutsch argues this blocked progress in foundations of physics for decades (see Bad Philosophy).
- Equivalent to anti-realism: Instrumentalism, consistently applied, denies that science gives us knowledge of a mind-independent reality. Deutsch holds this is simply false.