I expect that JamesR knows that and just wasn't being careful.
Yes, instrumentalism is typically an alternative to scientific realism. Sarkus and JamesR already know what I'm about to say, but it might be helpful for some of the others.
Examples of instrumentalism might be Ernst Mach's 19th century rejection of the reality of atoms [...]
"Brief" detour here into why Mach believed as he did (likewise only for those unfamiliar with it) and the putative connection of empiricists to the rival anti-realism of today.
Mach's version of positivism slash phenomenalism[1] probably got the denial of atoms from his later hero David Hume, who he (and just about everyone else) misconstrued as closing the door to the micro scale. Treating it as metaphysical territory that science could not address.
David Hume: My intention never was to penetrate into the nature of bodies, or explain the secret causes of their operations. For besides that this belongs not to my present purpose, I am afraid, that such an enterprise is beyond the reach of human understanding, and that we can never pretend to know body otherwise than by those external properties, which discover themselves to the senses. As to those who attempt any thing farther, I cannot approve of their ambition, till I see, in some one instance at least, that they have met with success. But at present I content myself with knowing perfectly the manner in which objects affect my senses, and their connections with each other, as far as experience informs me of them. This suffices for the conduct of life; and this also suffices for my philosophy, which pretends only to explain the nature and causes of our perceptions, or impressions and ideas. --An Enquiry Concerning Human Understanding
Of course, even in that paragraph Hume didn't absolutely close the door.
Nor did Kant in "Prolegomena To Any Future Metaphysics", which was Mach's first inspirational read prior to Hume's work. Kant plainly stated that science would continue to make unlimited progress in its investigation of the phenomenal or represented world. Atoms and quantum fields belong to that empirical world (are potentially real in that context), just like cosmological items at the other end of the scale (black holes, galaxies, etc).
Immanuel Kant: As long as the cognition of reason is homogeneous, definite bounds to it are inconceivable. In mathematics and in natural philosophy human reason admits of limits, but not of bounds, viz., that something indeed lies without it, at which it can never arrive, but not that it will at any point find completion in its internal progress. [...] Nor does that science require this for its physical explanations. Nay even if such grounds should be offered from other sources (for instance, the influence of immaterial beings), they must be rejected and not used in the progress of its explanations. For these explanations must only be grounded upon that which as an object of sense can belong to experience, and be brought into connexion with our actual perceptions and empirical laws.
But Mach was seduced by the general interpretation (around even back then) that empiricists (like Hume) inherently regarded the scale of atoms and beyond as metaphysical (that such entered into Plato's non-sensible realm or Kant's later noumenal rendition). Again, that's arguably not the case:
Silvio Seno Chibeni: What is little noticed in the literature is that many, if not most, of the leading figures the so‑called “empiricist” school of philosophy, such as Locke, Berkeley and Hume, did not see their epistemological position as necessarily ruling out this age‑old goal of science. In contrast with their classical predecessors, however, contemporary empiricists tend to assume that empiricism would automatically render impossible any defence of scientific realism.
I have argued elsewhere that this is a mistake (CHIBENI, 1997). Empiricism should be taken as a thesis on the foundations of knowledge, whereas realism is a thesis on its limits, or extension. But the association of empiricism with anti‑realism is now so widespread in the literature in the philosophy of science that scientific anti‑realism is often called “empiricism”.
Such misleading use of the term is common not only among the anti‑scientific realists (e.g. van Fraassen’s “constructive empiricism”), but also among the scientific realists themselves (see e.g. BOYD, 1984). This is quite surprising, for if the “empiricists” are identified, in the debate, with the anti‑realists, the scientific realists would be left in the uncomfortable position of being, perhaps, identified with the rationalists – the classical, and proper, opponents of the empiricists. But nowadays apparently nobody would feel comfortable in being classed as a “rationalist” in philosophy of science. --Hume On Unobservable Entities
- - - footnote - - -
[1] See the Edward S. Reed quotes
at the bottom of this post, with respect to what the brand of "phenomenalism" is that many 19th-century scientists indulged in. Note that the following Mach quote here will also clarify Reed's misunderstanding of their fundamental "sensations" as being subjective or mind-dependent, which they were not.
How Mach escaped solipsism is explained in his "The Analysis of Sensations".
Like Hume, Mach believed the human mind/body was only a bundle of sensations just as any other object was. (IOW, today's "qualia" were building components that were prior in rank to an emergent mind, and not dependent attributes of the latter). After death that was it -- there was no fundamental ego to begin with, and no "things in themselves" (no physical entities or Platonic abstractions) that the appearances or manifestations of the world corresponded to. Even though sensations ("qualia") were primary in this scheme, mind/ego was not.
Ernst Mach: For us, therefore, the world does not consist of mysterious entities, which by their interaction with another, equally mysterious entity, the ego, produce sensations, which alone are accessible. For us, colours, sounds, spaces, times, . . . are provisionally the ultimate elements, whose given connexion it is our business to investigate.
The ego is as little absolutely permanent as are bodies. [...] Thing, body, matter, are nothing apart from the combinations of the elements, - the colours, sounds, and so forth - nothing apart from their so-called attributes.
The primary fact is not the ego, but the elements (sensations). [...] The ego must be given up. It is partly the perception of this fact, partly the fear of it, that has given rise to the many extravagances of pessimism and optimism, and to numerous religious, ascetic, and philosophical absurdities...
[...] Bodies do not produce sensations, but complexes of elements (complexes of sensations) make up bodies. If, to the physicist, bodies appear the real, abiding existences, whilst the " elements " are regarded merely as their evanescent, transitory appearance, the physicist forgets, in the assumption of such a view, that all bodies are but thought-symbols for complexes of elements (complexes of sensations). Here, too, the elements in question form the real, immediate, and ultimate foundation, which it is the task of physiologico-physical research to investigate. By the recognition of this fact, many points of physiology and physics assume more distinct and more economical forms, and many spurious problems are disposed of. --The Analysis of Sensations