[5] The word "physicalism" was introduced into philosophy in the 1930s by Otto Neurath and Rudolf Carnap.
[11] These two theory-based conceptions of the physical represent both horns of Hempel's dilemma[12] (named after the late philosopher of science and logical empiricist Carl Gustav Hempel): an argument against theory-based understandings of the physical.
Frank Jackson, for example, has argued in favour of the aforementioned "object-based" conception of the physical.
David Papineau[17] and Barbara Montero[18] have advanced and subsequently defended[19] a "via negativa" characterization of the physical.
[20] Further, Restrepo argues that this conception of the physical makes core non-physical entities of non-physicalist metaphysics, like God, Cartesian souls and abstract numbers, physical, and thus either false or trivially true: "God is non-mentally-and-non-biologically identifiable as the thing that created the universe.
Supposing emergentism is true, non-physical emergent properties are non-mentally-and-non-biologically identifiable as non-linear effects of certain arrangements of matter.
The immaterial Cartesian soul is non-mentally-and-non-biologically identifiable as one of the things that interact causally with certain particles (coincident with the pineal gland).
To borrow a metaphor from Saul Kripke, the truth of physicalism at the actual world entails that once God has instantiated or "fixed" the physical properties and laws of our world, then God's work is done; the rest comes "automatically".
One response to this problem is to abandon (2) in favour of the possibility mentioned earlier in which supervenience-based formulations of physicalism are restricted to what David Chalmers calls "positive properties".
[32] Daniel Stoljar objects to this response to the blockers problem on the basis that since the non-physical properties of w1 aren't instantiated at a world in which there is a blocker, they are not positive properties in Chalmers's sense, and so (3) will count w1 as a world at which physicalism is true after all.
A necessary being is compatible with all the definitions provided, because it is supervenient on everything; yet it is usually taken to contradict the notion that everything is physical.
[22] Additional objections have been raised to the above definitions provided for supervenience physicalism: one could imagine an alternative world that differs only by the presence of a single ammonium molecule (or physical property), and yet based on (1), such a world might be completely different in terms of its distribution of mental properties.
[36] Another version of reductionism is based on the requirement that one theory (mental or physical) be logically derivable from a second.
Supervenience physicalism has been seen as a strong version of emergentism, in which the subject's psychological experience is considered genuinely novel.
[2] Non-reductive physicalism, on the other side, is a weak version of emergentism because it does not need that the subject's psychological experience be novel.
Rather, they would hold that the inference from PTI to N is justified by metaphysical considerations that in turn can be derived from experience.
[42] At a rough approximation, the conceivability argument runs as follows: P1) PTI and not Q (where "Q" stands for the conjunction of all truths about consciousness, or some "generic" truth about someone being "phenomenally" conscious [i.e., there is "something it is like"[43] to be a person x] ) is conceivable (i.e., it is not knowable a priori that PTI and not Q is false).
The a priori physicalist, then, must argue that PTI and not Q, on ideal rational reflection, is incoherent or contradictory.
[45] A posteriori physicalists, on the other hand, generally accept P1) but deny P2)--the move from "conceivability to metaphysical possibility".
Some a posteriori physicalists think that unlike the possession of most, if not all other empirical concepts, the possession of consciousness has the special property that the presence of PTI and the absence of consciousness will be conceivable—even though, according to them, it is knowable a posteriori that PTI and not Q is not metaphysically possible.
These a posteriori physicalists endorse some version of what Daniel Stoljar (2005) has called "the phenomenal concept strategy".
[47] Other a posteriori physicalists[48] eschew the phenomenal concept strategy, and argue that even ordinary macroscopic truths such as "water covers 60% of the earth's surface" are not knowable a priori from PTI and a non-deferential grasp of the concepts "water" and "earth" et cetera.
[51][52][53] Strawson argues that "many—perhaps most—of those who call themselves physicalists or materialists [are mistakenly] committed to the thesis that physical stuff is, in itself, in its fundamental nature, something wholly and utterly non-experiential... even when they are prepared to admit with Eddington that physical stuff has, in itself, 'a nature capable of manifesting itself as mental activity', i.e. as experience or consciousness".
[51] Because experiential phenomena allegedly cannot be emergent from wholly non-experiential phenomena, philosophers are driven to substance dualism, property dualism, eliminative materialism and "all other crazy attempts at wholesale mental-to-non-mental reduction".
This sounded crazy to me for a long time, but I am quite used to it, now that I know that there is no alternative short of 'substance dualism'... Real physicalism, realistic physicalism, entails panpsychism, and whatever problems are raised by this fact are problems a real physicalist must face.
[51]Christian List argues that Benj Hellie's vertiginous question, i.e. why a given individual exists as that individual and not as someone else, and the existence of first-personal facts, is evidence against physicalist theories of consciousness and against other third-personal metaphysical pictures, including standard versions of dualism.
[54] List also argues that the vertiginous question implies a "quadrilemma" for theories of consciousness, where no theory of consciousness can simultaneously respect four initially plausible metaphysical claims – namely, "first-person realism", "non-solipsism", "non-fragmentation", and "one world" – but that any three of the four claims are mutually consistent.