This is a continuation of yesterday's post. Yesterday I identified what seemed to me to be a problem for the way that Ted Sider wanted to explain why various macro-level things are more privileged—basically, they're said to be more joint-carving. But as I said yesterday, I just don't see that they are.
I suspect, however, that one can get something quite a bit like Sider's picture here if one is willing to add a bit more structure. The prospects for a reasonable purely physical story about chemical objects and properties seem reasonable. It doesn't seem hopeless to try to give a reasonably simple definition of molecule or magnesium or valence in purely physical terms. So if we assume the (absolute) fundamentality of physics, we can run the story Sider wants for why we refer to molecules instead of molecules-or-cucumbers, or even molecules-before-2013-and-regions-of-space-afterwards, because the physical definition of molecule is significantly simpler than these more bizarre properties. (In the former case, a purely physical definition will be insanely complex, as in the case of pig; in the latter, it will still be not insanely complex, but more complex than that for molecule.)
This is basically just a way of expressing the familiar idea that chemistry somehow reduces to, or emerges from, physics. But if we buy into Ted's general ideas, we can add this: it is part of the objective structure of the world that chemical properties are related to physical properties in this way. The 'book of the world' will give us the chemical on top of the physical (and the chemical is objectively privileged over the schmemical).
Now what happens when we go up another level? It's pretty natural to suppose that cell biology relates to chemistry as chemistry does to physics. So --- and here's where the picture I'm describing departs from Ted's --- when adjudicating between which objects we refer to in our discourse about cell biology, objects with reasonably simple definitions in chemical terms --- not physical terms --- are privileged over ones that don't. We don't always go back to the most fundamental; we just go back to the more fundamental domain that is appropriate for the matter at hand. Often, but not always, the simpler definition is the more fundamental theory will correspond to the simpler definition in the ultimately fundamental theory; when it doesn't, I think we should go with the less fundamental one. (It's having a better chemical account that makes a particular referent of 'cell' the preferred one, not having a better physical account.)
The reason I'm interested in this, besides the fact that it's interesting, is that I'm leaning in this kind of a direction as a way of making sense of what the 'knowledge first' attitude is. (Yes, I'm reading metaphysics, but it's in the service of epistemology, I swear!) I understand it as a metaphysical thesis: knowledge is a more fundamental state than has been traditionally recognized. In the terms of this broad way of thinking about theorizing about the world, knowledge shows up at a more fundamental level than one might have thought. (Compare a 'life first' theorist, who thinks that the attempt to define life in biological terms is a mistake; life's home is really at the chemical level—we need to invoke life to understand, say, combustion.) How early should knowledge appear? Presumably, people could differ about this. If you wanted to, you could think that knowledge was perfectly fundamental; knowledge is as basic as quarks or whatever. You'd oppose any kind of reduction of knowledge to anything. This doesn't sound very plausible, but you could say that if you wanted to. My suspicion is that knowledge will be an important theoretical term from the basics of intentional psychology.