I can’t help feeling, @TheBJPS @StathisPsillos @WayneMyrvold, that we’re losing the wood for the trees in all these details about which positivist said what and when about unobservables. In truth, a huge sea-change took place in our philosophical tradition in the 20C. 1/x

We’ll misunderstand older views if we lose sight of it. Throughout the 19C, pretty much all philosophers assumed that reality was exhausted by what is directly accessible in experience. Neo-Kantians, naturphilosophie, Mill, Mach, Moore and Russell, A J Ayer, . . . 2/x

We need to remember by the late 19C microphysics had ceased to be part of serious science. While the 17C had been committed to an underlying microphysics, no good microphysical theories had been established, and their falling outside serious discourse was bolstered by . . . 3/x

. . . Newton’s “hypotheses non fingo” and various forms of concept empiricism and Kantianism. Then along came atomic theory, germ theory, electromagnetic theory. Philosophers were slow to take them seriously. 4/x

“Stories told by scientists that we might look at once we’ve sorted out the nature of lived reality.” (Students from Europe sometimes still say this when it’s suggested their views are in tension with physicalism.) 5/x

In time, of course, the analytic tradition flipped, and now the aim is to understand how the world is grounded in microphysical reality, not in elements given of experience. To be simple-minded, I’d say the change happened once we had philosophers who’d been . . . 6/x

. . taught atomic chemistry at school. If you grow up believing atomic chemistry, then you can’t think the basic constituents of reality are experiential givens. Of course, the older logical positivists in the Vienna Circle were serious people familiar with current science. 7/x

So they strove to make space for microscopic unobservables. But it was against a philosophical background that ruled it impossible to refer to an unobservable reality behind the appearances. That’s why you find Schlick running the line . . . 8/x

. . that there’s no substantial difference between realists and intrumentalists, and still find neo-positivists struggling, well into the 1960s, to accept that microphysical theories really say what they do say, as opposed to just predicting observable appearances. 9/9