Questions: Instrumentalism

Question 1

Newtonian mechanics and quantum mechanics make incompatible claims about the underlying structure of the physical world, yet both yield accurate predictions within their domains. An instrumentalist would interpret this situation by saying:

• A. One theory must be true and the other false; we should determine which one accurately describes reality
• B. Both are approximately true descriptions of reality, so we should try to unify them into a single true theory
• C. The question of which theory is 'really true' is misguided; both are valid instruments insofar as they reliably map inputs to correct predictions in their domains
• D. Quantum mechanics is correct because it gives more accurate predictions, which confirms scientific realism

Answer: (C)

The instrumentalist reinterprets what theories *are*: not true-or-false pictures of hidden reality, but inferential tools that organize observations into predictions. Just as different maps of the same terrain (topographic, road, satellite) serve different purposes without any being 'the true map,' different theories can serve different predictive purposes. The instrumentalist does not ask which theory truly describes the world — that question presupposes a kind of metaphysical access that instrumentalism denies we have.

Question 2

What is the 'no-miracles argument,' and why is it the central challenge to instrumentalism?

• A. It argues that scientists are unlikely to all be systematically deceived, so scientific consensus must be tracking truth
• B. It argues that if scientific theories were not approximately true descriptions of reality, their success — especially their novel predictions — would be an inexplicable miracle; their success demands a realist explanation
• C. It claims that the improbability of scientific progress proves theories reflect hidden necessary order in nature
• D. It argues that successful theories that survive testing have been miraculously confirmed by nature

Answer: (B)

The no-miracles argument (associated with Hilary Putnam) holds: if our best theories were mere computational devices with no connection to reality, why do they succeed so spectacularly — including in predicting phenomena that weren't observed when the theory was formulated? The instrumentalist response is typically that we only retain theories that work (selection effect), so there's nothing surprising about our current theories succeeding. The debate centers on whether novel predictive success can be explained without positing approximate truth.

Question 3

Under instrumentalism, Ptolemy's epicycles were a successful scientific achievement even though they were wrong about the structure of the solar system.

• T. True
• F. False

Answer: True

This is precisely the kind of historical case instrumentalists find compelling. Epicycles made accurate astronomical predictions for over a thousand years — they were, by the instrumentalist's criterion (predictive success), genuinely successful. The instrumentalist would say asking whether they were 'really true' about planetary motion is the wrong question. What mattered was that they reliably served the purpose of a scientific theory: generating correct predictions. Their later replacement by Copernican and then Newtonian models was a practical improvement in predictive power, not a revelation that the true underlying structure had finally been found.

Question 4

Instrumentalism holds that scientific theories should be evaluated primarily by their mathematical elegance and internal consistency, setting aside predictive accuracy.

• T. True
• F. False

Answer: False

This reverses the instrumentalist position. Instrumentalism evaluates theories *by* their predictive success — their ability to reliably map observational inputs to correct outputs. Elegance and consistency are, at most, instrumental virtues (they make theories easier to use) rather than epistemic virtues (they don't indicate truth). A mathematically inelegant theory that predicts correctly is, for the instrumentalist, a better theory than a beautiful one that doesn't.

Question 5

An instrumentalist and a scientific realist both agree that quantum electrodynamics (QED) makes extraordinarily accurate predictions. Where exactly do they disagree, and why does it matter?

Model answer: The realist holds that QED's predictive success is evidence that it approximately describes how reality actually is — that virtual particles, quantum fields, and the formalism reflect real features of the unobservable world. The instrumentalist holds that QED is a supremely effective tool for predicting measurement outcomes, but we have no grounds to conclude it describes hidden reality; its success tells us it works, not that it is true. The disagreement matters because it affects how we interpret theory change (are we getting closer to truth, or just building better tools?), how we understand the relationship between theories in different domains, and what we take to be the ultimate goal of science.

A practical consequence: the realist is committed to taking the ontology of QED seriously — there really are fields, virtual particles, etc. The instrumentalist can remain agnostic about whether these posits refer to anything, treating them as useful fictions in a predictive calculus.