= Solution
<Instrumentalism> treats theoretical descriptions primarily as tools for organizing and predicting observations rather than as a literally true inventory of <unobservable entities>. Its attraction is epistemic economy: where empirical success is all the evidence establishes, using a successful calculation need not commit us to every mechanism appearing in it. The abandonment of <phlogiston> illustrates why such caution can be reasonable.
However, distinguish three claims: we can use a theory without believing it; we ought to suspend belief about some of its entities; and those entities do not exist or theoretical sentences are not truth-apt. The first is commonplace and does not establish the last two. <Constructive empiricism> interprets theoretical claims literally while distinguishing acceptance for <empirical adequacy> from belief in the whole theory. It therefore offers restraint without treating all theoretical language as a disguised calculation recipe.<Constructive Empiricism Now by Bas van Fraassen>[section III: acceptance and belief]{ref}
A <scientific realist> can answer that independent experimental access, successful interventions and unexpectedly accurate new predictions support some entities more strongly than mere curve fitting. The <no-miracles argument> treats this convergence as something needing explanation. The reply is not conclusive: explanatory success need not guarantee truth, and selectively retained successful theories can make retrospective success look stronger than it was. Equally, historical failures do not show that every present theoretical commitment is equally fragile.
There is therefore a good argument for instrumental use and selective suspension of belief where evidence does not discriminate ontologies. There is a weaker argument for universal <instrumentalism> about every scientific entity. A defensible position should compare the actual evidence for particular commitments and explain why empirical adequacy is the right stopping point, rather than infer global agnosticism from the bare possibility of error.
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