Yes, thank you for clearing up your point. I think that @orthonormal hit the nail on the head. What I meant to get at was not that my conversation partners care very much whether we can conclusively say that something does/doesn't underlie amplitude. It's more that they have their own favorite phenomena which they want to have similar status as quantum amplitude. It could be the power of prayer, the rightness of a political ideology, etc. They engage in the regress of "well what's that made out of" only so that when I hit something at the bottom (currently amplitude), then they can say that separate magisteria allows them to claim with equal validity that their favorite phenomena are just like amplitude and are ontologically basic.
Really this about looking at any two phenomena we can observe and saying that there is some finer level that underlies them both and explains them. Many who dispute that want to press you about whatever the limits of knowledge are in physics and then argue that this justifies their metaphysical views that some other thing cannot be reduced.
On a tangent, this makes me wonder what has been said about mathematical models of the levels of abstraction/semantic resolution of reality. Is there any kind of meaningful total ordering of these levels? Could the different levels of reductionism be partially ordered? Are they observer-dependent. These are interesting questions.
I have read the sequences on reductionism and quantum physics some time ago now and I was hoping for some help finding the right places to go back and re-read there to address a question. If the way I describe my question reveals other ignorance on my part, please feel free to add comments above and beyond sequence references.
When trying to talk a little about reductionism, most (non-LW) people I speak to seem to want to play the following game:
What's an airplane made out of? Molecules and atoms that comprise materials like metal, plastic, glass, rubber, etc. What are molecules and atoms made out of? Well, molecules are collections of atoms bonded together, and atoms are made up of three basic particles: protons, neutrons, and electrons. What are basic particles made out of? Well, here things start to get a little more dicey. Some of the basic particles are known to be made up of even smaller sub-atomic elementary particles, such as quarks, leptons, and bosons. Some of the basic particles are examples of these elementary particles. Well, what's an elementary particle made of? Well, that's a pretty tough one, but basically there's this sort of fabric of stuff underlying everything called quantum amplitude, and a certain configuration of quantum amplitude corresponds to an elementary particle. So what's quantum amplitude made up of? Well, I'm not sure that is a coherent question. It just sort of is. A ha! I've caught you. So ultimately way down at the bottom of it all, you're telling me that some something "just exists" (i.e. is ontologically basic). But then why do you call it reductionism if it ultimately boils down to a Platonistic ideal of quantum amplitude (no one actually says this, but it's my translation of the objections I tend to face).
Is it more or less right to say that, as far as we can tell, the only reasonable thing to which we can attribute ontologically basic status is quantum amplitude? Given that amplitude is a mathematical device that allows calculation of probability, and probability describes my ignorance about the world (i.e. my best guess as to what the territory is, as opposed to the actual territory), do we view quantum amplitude as some sort of pre-states-of-knowledge concept? How does that mesh up with "what is an elementary particle made of?" It makes me want to call it "the residue of intrinsic uncertainty" or something, but why would that "really exist?" I don't think that my uncertainty about tomorrow's weather "really exists" in any Platonistic way.
How do you explain to people that reductionism = (reduce until you have good reason not to); am I even right to say that or is this a harmful oversimplification?