= Solution
The replacement is philosophically significant because it challenges the inference from a theory's practical success to the existence of its proposed entities. <Phlogiston theory> interpreted ordinary <combustion> and metallic calcination as the loss of <phlogiston>; the <oxygen theory of combustion> instead treated these processes as combination with <oxygen>. This changes the account of what matter is doing, not merely the spelling of an agreed substance. <Antoine Lavoisier>'s systematic treatment links the new chemistry with quantitative <mass> accounting and a revised <chemical nomenclature>.<Elements of Chemistry by Antoine Lavoisier>[Preliminary Discourse and part I, chapters III–V]{ref}
For <scientific realism>, the difficulty is that a once-useful theoretical term may fail to refer. If earlier success coexisted with a nonexistent <unobservable entity>, present success alone cannot guarantee that every central term of our theories refers either. This is the force of the <pessimistic induction>; it rebuts an unrestricted success-to-truth inference rather than deductively proving every present theory false.<A Confutation of Convergent Realism by Larry Laudan>[discussion of historical counterexamples to success implying reference]{ref}
Several replies reduce, but do not erase, the problem. A <scientific realist> can distinguish successful empirical regularities from the particular mechanisms used to explain them, retaining only claims independently supported by varied <experiments>. <Structural realism> can emphasize preserved quantitative relations; it must identify the actual relations and their physical interpretation rather than declaring any recurring mathematics a vindication. A causal account of reference may preserve a term across some mistaken descriptions, but it cannot automatically identify <phlogiston> with <oxygen>: their proposed roles in the reaction differ.
A defensible conclusion is therefore selective and fallible <scientific realism>. The historical episode motivates stricter criteria for commitment, including independent manipulation, cross-checks and successful novel tests. It does not force the view that all theoretical entities are mere instruments. Conversely, calling the abandoned theory approximately true without specifying which claims survived simply restates the difficulty.
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