The antidote is the realisation that not just certainty, but also doubt, requires justification. — Banno
You seem to be arguing here for a critical rationalism, which I also support. But that's an epistemological position (which particular beliefs are justified), not an ontological position (what even is it for something to be real). The two are not in conflict, and are in fact necessitated by the same deeper principles.
Empiricism is necessitated by the same principle that necessitates rationalism more generally: every answer must be questionable, which means not taking anything on faith, which means not entertaining claims about anything that can't be tested.
Meanwhile objectivism is necessitated by the same principle that necessitates
critical rationalism specifically: every question has an answer, which directly entails objectivism, but also demands a rejection of justificationism, as that leads via infinite regress to nihilism, leaving only the options of fideism, which we've already ruled out above, or else critical rationalism.
In any case, I'm not arguing for empirical realism from a place of Cartesian doubt. I haven't actually presented much of an argument here at all, merely an exploration of the relation of empirical realism to other threads of philosophical thought, including Spinoza (it's a neutral monism but not like his), Mill (it's much like his ontology), Descartes, Gassendi and Lichtenberg (it's not like Descartes because of the reasons Gassendi and Lichtenberg give), and Whitehead (it's very much like his ontology).
My argument for this position would just be an argument against nihilism (including solipsism, relativism, and subjectivism), and an argument against transcendentalism (meaning in this case basically supernaturalism), leaving us with the position that there are objective answers to questions about reality, but that those answers consist entirely of claims about the kinds of experiences there are available to be had in what circumstances.
How can mind-like stuff be just the activity of brains — Banno
"Mind-like stuff" is not the activity of brains, on my account. Actual
minds are. "Mind-like stuff" is a loose way of saying essentially "information": it's the kind of stuff that minds process. Minds, being the behavior of brains, are made of that same stuff, because all physical stuff is. In a computer, every program is made of data, and what those programs act upon is more data. I'm saying reality is analogous to that, or maybe not even so distant as to be an analogy. Reality is made of information, of the kinds that minds process, but information that exists whether or not minds are there to be processing it; minds, being (behaviors of) real physical things like anything else, are made out of that same information, that they then process. The data is first, execution of the data comes later, and only certain data constructs do any interesting data-processing when executed; most just crash. (Which is why not all this information-stuff reality is made of exhibits consciousness like we normally think of it, despite being made of the same stuff as brains that can be conscious; it's not structured correctly, into a thinking machine. It's data that doesn't do anything interesting when executed).
Are they particles, and hence Pfhorrest is a realist, or are they "occasions of experience", and hence Pfhorrest is an idealist? — Banno
a vicious little circle if ever there was one — Banno
"Minds are an action of physical things, but physical stuff is made of ideas in minds"... sure, that's a primitive way I once thought of this line of thought decades ago, when I was tempted by both idealism in ontology class and materialism in philosophy of mind class.
The resolution to that apparent conflict is neutral monism. There isn't mental stuff and material stuff, or just one or the other, but a neutral stuff that's kinda both or neither. Physical stuff is phenomenal stuff, the kind of stuff you can empirically observe, but that isn't dependent on you observing it, that is independent of your particular subjective experience, without being something completely beyond all possibility of being experienced.
One direction away from that position lies supernaturalism, believing in stuff that can't possibly be observed, the existence of which could only be taken on faith, but "it's really objectively real I swear" if you do take it on faith. In the other direction away from it lies some kind of subjectivism, relativism, solipsism, or nihilism, denying that there is any reality to the stuff you experience beyond
your experiencing of it, such that it would cease to exist if you did. Carefully avoiding anything like either of those leaves you where I am: empirical realism, or physicalist phenomenalism, or anti-supernaturalist anti-solipsism if you really prefer.