In discussing strategies for avoiding epiphenomenalism (the idea that subjective experience is causally irrelevant), David Chalmers lists one option as (The Conscious Mind, 1996, p. 153):
4. The intrinsic nature of the physical. The strategy to which I am most drawn stems from the observation that physical theory only characterizes its basic entities relationally, in terms of their causal and other relations to other entities. Basic particles, for instance, are largely characterized in terms of their propensity to interact with other particles. Their mass and charge is specified, to be sure, but all that a specification of mass ultimately comes to is a propensity to be accelerated in certain ways by forces, and so on. Each entity is characterized by its relation to other entities, and these entities are characterized by their relations to other entities, and so on forever (except, perhaps, for some entities that are characterized by their relation to an observer). The picture of the physical world that this yields is that of a giant causal flux, but the picture tells us nothing about what all this causation relates. Reference to the proton is fixed as the thing that causes interactions of a certain kind, that combines in certain ways with other entities, and so on; but what is the thing that is doing the causing and combining? As Russell (1927) notes, this is a matter about which physical theory is silent.
One might be attracted to the view of the world as pure causal flux, with no further properties for the causation to relate, but this would lead to a strangely insubstantial view of the physical world. It would contain only causal and nomic relations between empty placeholders with no properties of their own. Intuitively, it is more reasonable to suppose that the basic entities that all this causation relates have some internal nature of their own, some intrinsic properties, so that the world has some substance to it. But physics can at best fix reference to those properties by virtue of their extrinsic relations; it tells us nothing directly about what those properties might be. We have some vague intuitions about these properties based on our experience of their macroscopic analogs – intuitions about the very “massiveness” of mass, for example – but it is hard to flesh these intuitions out, and it is not clear on reflection that there is anything to them.
There is only one class of intrinsic, nonrelational property with which we have any direct familiarity, and that is the class of phenomenal properties. It is natural to speculate that there may be some relation or even overlap between the uncharacterized intrinsic properties of physical entities, and the familiar intrinsic properties of experience. Perhaps, as Russell suggested, at least some of the intrinsic properties of the physical are themselves a variety of phenomenal property? The idea sounds wild at first, but on reflection it becomes less so. After all, we really have no idea about the intrinsic properties of the physical. Their nature is up for grabs, and phenomenal properties seem as likely a candidate as any other.
It doesn’t matter if one postulates a “pure causal flux” or not. The reason is that the way we understand both things and their relations (or causality) is representational. If one is going down this road, then subjective experience could be identified with the ‘hidden’ aspect of the things, or the ‘hidden’ aspect of the relations.
In physical representation, one has an abstract, quantitative representation of things in a space, say. The relations are abstract as well as the things. That is to say, our representations of extrinsic properties presumably correlate to something real, but there is ‘room’ to put subjective experience ‘in’ behind the representations, as well.
This is to say, if we think that we have a direct line to (in some sense) non-representational knowledge of our own subjective experience, then it is not clear why that subjective experience can’t be identified with either the extrinsic, intrinsic, or both sorts of physical properties.
So when Chalmers says that there “is only one class of intrinsic, nonrelational property with which we have any direct familiarity, and that is the class of phenomenal properties,” this may be wrong. Chalmers is assuming a ‘relevant transparency‘ when it comes to representations of relations, but not to things. Phenomenal properties may turn out not to be ‘intrinsic’ or ‘nonrelational’.