Reply to Doctor Logic
DL: It seems that Feser is making at least two mistakes.
First, were we to study protons, neutrons and electrons, we would find that they are not flammable. Flammability is found in the interactions of vastly complex structures of these particles. So, how can it be that protons, neutrons and electrons, which cannot be flammable can explain why gasoline burns?
Well, it is quite obvious that flammability is built upon complex configurations of these building blocks, and flammability only makes sense in that context. You will never be able to assign an intrinsic property of a configuration of components to an individual component. So it is with mental properties. If mental properties are founded on complex configurations on a material substrate, you shouldn't expect to see mental properties in individual particles, or even individual subsystems like neurons.
Second, Feser is losing track of his definitions. Intentionality is defined by our experience of intent. It is not defined by its non-material nature. If physicalism is correct, then intentionality does not become an illusion. It is only the belief that intentionality is non-material that becomes an illusion. Intentionality remains as it has always been, and as important to us as it has always been.
VR: Configurations, I will grant, give us states at the configurational level that are not mentioned in a description of the proper parts. However, the configurational properties are transparent given the locations of constituent parts. So no brick is six feet high, but if they all are put together in a wall, the wall can be six feet high even though the bricks are not. Given where the bricks are, it follows necessarily how high the wall is. The wall-states are fully determined by the brick states.
In the case of intentionality, intentional states are underdetermined by physical states. Add up all the physical states you like, and the result is logically compatible with there being different mental states, or with there being no mental states at all. If we look at the output of a computer, it is not just the computer that is doing such and such with such and such a meaning, we interpret it as having that meaning.
You say "intentionality is defined by our experience of intent." Gosh I hope not. If we don't know what intentionality is, how in blazes are we going to be able to identify our experience of intent. More importantly, intentionality, in philosophy of mind, always refers to "aboutness," not purposiveness. What is it about one physical state that makes it about another physical state? That's the question being dealt with here.