«During the last two decades there has been a resurgence of arguments against physicalism and for varieties of metaphysical dualism. The conclusion of ...»
Illuminati, zombies and metaphysical gridlock1
During the last two decades there has been a resurgence of arguments against physicalism
and for varieties of metaphysical dualism. The conclusion of these arguments is that phenomenal
consciousness is absent from a world that is purely physical. Many contemporary philosophers of
mind have found some of these arguments to be persuasive and have opted for some form of
anti-physicalism.2 In this paper I will survey the landscape of these arguments and physicalist responses to them. The anti-physicalist arguments that I discuss start from a premise about a conceptual, epistemic, or explanatory gap between physical and phenomenal descriptions3 and conclude from this – on a priori grounds – that physicalism is false.4 I call these arguments 1 I would like to thank Ned Block, David Chalmers, Troy Cross, Tamar Gendler, Barry Loewer, Raymond Martin and Gilad Tanay, participants of a discussion group at NYU, and an audience at the Rutgers University philosophy department for comments and helpful discussion of this paper.
2 David Chalmers’ recently compiled list of contemporary anti-physicalists includes Joseph Almog, Torin Alter, George Bealer, Laurence BonJour, Paul Boghossian, Tyler Burge, Tim Crane, John Foster, Brie Gertler, George Graham, W.D. Hart, Ted Honderich, Terry Horgan, Steven Horst, Jaegwon Kim, Saul Kripke, Harold Langsam, E.J. Lowe, Kirk Ludwig, Trenton Merricks, Martine Nida-Rümelin, Adam Pautz, David Pitt, Alvin Plantinga, Howard Robinson, William Robinson, Gregg Rosenberg, A.D. Smith, Richard Swinburne, and Stephen White. From his BLOG “Fragments of Consciousness” September 26, 2005.
3 Phenomenal descriptions attribute phenomenal properties to experience (and perhaps to thought) in the sense of there being something it is like to undergo an experience, something one can normally introspect, e.g., the feeling of my fingers flexing that (partly) characterizes my present bodily sensation. I will assume throughout the paper that there are phenomenal properties in this sense. For eliminativism about phenomenal properties, see, e.g., Rey (2007).
4 These arguments include, among others, arguments based on conceivability considerations by Kripke (1972), Nagel (1974), Bealer (1994), Chalmers (1996, and 2009), as well as the Knowledge Argument of Jackson (1982), versions of the Property dualism Argument in Robinson (1993), White (2007), and Nida-Rümelin (2007), and the Explanatory Gap Argument in Levine (2001) and (2007).
1 “conceivability arguments”. Although not all of them have a premise concerning conceivability,5 they all, if successful, establish that it is inconceivable that phenomenal experience exists in a purely physical world. My first aim is to develop a master argument to counter these arguments.
Along the way I develop a new version of one of these arguments – Chalmers’ Zombie Argument – that is immune from objections that I have previously urged against the original argument, based on a distinction between positive and negative conceivability. However, I will show that there is a master argument that provides an adequate physicalist response both to the new Zombie Argument and to the other anti-physicalist conceivability arguments. The master argument is crucially bolstered by what has come to be known as the Phenomenal Concept Strategy6; this strategy – following Brian Loar’s original proposal in (1997) – appeals to the special cognitive features of phenomenal concepts in providing a physicalistically respectable explanation of the aforementioned gaps. What is new in my appeal to the Phenomenal Concept Strategy is to harness the strategy – together with holistic considerations about which metaphysical framework is more virtuous in terms of simplicity and explanatory power – to be part of a formal argument to be used to rebut any gap-based argument. I propose such an argument and consider objections to it from the anti-physicalist side.
In the second part of the paper I assess the dialectical situation created by such a general physicalist reply to the anti-physicalist arguments, and argue that, despite the fact that a satisfactory reply can be given to the conceivability arguments, there is a puzzling symmetry between dualist attacks on physicalism and physicalist replies. Each position can be developed in a way to defend itself from attacks from the other position; I will argue that there are neither a priori nor a posteriori ways to decide between the two.
The plan is as follows. Section I provides background for the conceivability arguments.
Section II discusses David Chalmers’ Zombie Argument and my refutation of that argument. In Section III and IV I develop a new interpretation of Chalmers’ idea of positive conceivability7 and formulate a version of Chalmers’ argument that – along with a number of other conceivability arguments - is immune to my refutation of Chalmers’ original argument. In section V and VI, I develop a physicalist master argument – I will call it the Counter Conceivability Argument – that takes into account these refinements and rebuts all versions of the conceivability argument. In Section VII, I discuss a physicalist strategy, the Phenomenal Concept Strategy, which complements and supports the Counter Conceivability Argument. In the final section of the paper I argue that there is a structural similarity between the anti-physicalist and physicalist strategies: they are both able to defend themselves from the attacks of the other 5 I will later introduce and explicate two notions of conceivability.
6 Stoljar (2005) introduced this phrase.
7 My explication of positive conceivability differs from that of Chalmers (2002a).
2 side, but they both can be viewed as question-begging from the other side. In conclusion I will examine what this means for the status of the mind-body problem.
I. Metaphysical background
The debate between physicalism and anti-physicalism is a debate about fundamental ontology. According to physicalism, the world’s fundamental ontology is physical.8 It is not easy to say exactly what makes fundamental entities and properties “physical.” But this isn’t a problem since it suffices for our discussion that physicalism is understood as requiring that fundamental physical properties and entities are “non-mental.” So if physicalism is true then fundamental physical properties and entities do not exhibit intentionality and consciousness (and they do not even exhibit proto-mental proto-intentionality or proto-consciousness); intentionality and consciousness is instantiated only in macroscopic systems in virtue of immensely complex arrangements of fundamental properties and entities and their causal/nomological features; i.e.
for biological individuals in virtue of brain states and processes.
Anti-physicalism comes in a number of different varieties.9 I will be explicitly concerned with non-interactionist property dualism.10 Non-interactionist property dualists don’t necessarily deny mental causation but they – unlike interactionist dualists – accept the causal closure of physics. According to non-interactionist property dualism the fundamental ontology of the world includes mental and/or proto-mental properties.11 This means that arrangements of fundamental 8 Contemporary physicalists typically hold that the best account of that ontology is provided by fundamental physics. Physics’ best hypotheses about fundamental ontology is that it consists of elementary particles, strings and/or fields occupying a space-time structure, and possessing a limited number of quantitative properties (mass, charge, electromagnetic potential, and so on).
Physics also claims that there are only a few fundamental dynamical and perhaps non-dynamical laws that govern the structure of space-time and the evolution of its occupants.
9 The usual suspects include idealism, interactionist property or substance dualism, noninteractionist property or substance dualism and Russellian Monism.
10 I find substance dualism problematic for reasons that are beyond the scope of this paper.
Interactive property dualism is implausible since it requires a denial of the causal closure of physics. I will not be explicitly concerned with Russellian monism in this paper; but I think the points I make with respect to non-interactionist property dualism can be equally made with respect to Russellian monism as well.
11 Proto-mental properties are not full-blown mental properties; but they are constituents of fullphysical entities and their physical properties are not metaphysically sufficient for the instantiation of phenomenal properties. Non-interactionist property dualism grants that the physical realm is nomologically closed, and it posits the existence of fundamental vertical laws12 that connect arrangements of physical entities and properties to phenomenal properties. From now on, by “dualism” I mean this view.
Following Frank Jackson, I will assume that there is a fundamental vocabulary (although not necessarily in our language as it is currently) in which there is a complete fundamental true description of the world. This description specifies the total spatio-temporal distribution of fundamental entities, the totality of instantiations of fundamental properties and relations, and the fundamental laws. If physicalism is true then none of the elementary vocabulary refers to mental entities or properties. Jackson pointed out that a necessary condition for the truth of physicalism in a world is that all positive truths in that world, including, as it may be, positive truths about phenomenal consciousness,13 are metaphysically necessitated by the complete physical truth about that world.14 It follows that if physicalism is true in our world, the Physicalist Entailment blown mental properties.
12 I will assume that these laws are contingent; i.e., not metaphysically necessary. If laws are taken to be metaphysically necessary then it is difficult to state the difference between physicalism and dualism since then both would hold that configurations of physical property instantiations metaphysically necessitate mental property instantiations.
13 A positive phenomenal statement says that a phenomenal property is instantiated; e.g., Joe is feeling an itch. Negative truths, like There are no angels, and global statements, like Every gold cube has a volume smaller that one cubic meter, are not metaphysically necessitated by the complete physical truth about the world P although they are necessitated by P and a clause that says that P is the whole fundamental truth. However, the phenomenal and physical truths we will be interested in are all positive truths so I will ignore this complication for the remainder of the paper.
14 This formulation is based on Jackson’s (Jackson 1993). The first precise formulation of physicalism along these lines is due to Lewis (Lewis 1983a). Subsequent discussions are variations on the same theme. Many philosophers, among them non-physicalists, accept this formulation as capturing a very important component of the intuitive idea of physicalism. But it doesn't express the full physicalist commitment – only a necessary condition – because it is apparently compatible with certain ontologies that are intuitively non-physicalist e.g., with one in which there are fundamental mental as well as fundamental physical properties connected by “brute” necessary connections.
Thesis is true:
If there are mental truths – for example, that Mary knows what it is like to see red – that are not necessitated by the complete physical description then physicalism is false.
II. The Zombie16 Argument and the Zombie Refutation There is a line of argument going back at least to Descartes’ argument for the distinctness of mind and body that claims to show that physicalism is false. In fact, these arguments can be understood to conclude, on the basis of a priori considerations, that no world where phenomenal properties are exemplified can be a purely physical world. The descendent of this argument that has received the most attention in the last decade is David Chalmers’ “Zombie Argument.” Chalmers’ (Chalmers 2009) most recent formulation of the zombie argument is as
The Zombie Argument
1) P&~Q is conceivable. 17
2) If P&~Q is conceivable then P&~Q is metaphysically possible (CP principle)
3) If P&~Q is metaphysically possible then physicalism is false.
4) Physicalism is false.
15 ∀ is a substitutional quantifier, T is a statement variable for true positive statements, is the metaphysical necessity operator, and P is the complete fundamental physical description of the world, including the fundamental physical laws.
16 Zombies are creatures that are physically identical to normal humans but have no phenomenal experiences whatsoever.
17 P is the complete fundamental physical description of the world, including the fundamental physical laws, and Q is a positive phenomenal truth, e.g., that someone is having a visual experience with a particular phenomenal character at a particular time.
5 By “statement S is conceivable” Chalmers (1996) means “S cannot be ruled out a priori”.18 Thus conceivability for him is not a psychological but an epistemological notion. It may be psychologically impossible for us to imagine or see clearly that space has 11 dimensions but that doesn’t mean that it is inconceivable since it cannot be ruled out a priori. This is the basic notion of “conceivable” that I will be working with throughout much of the paper.
Chalmers (2002) distinguishes it from another notion of conceivability – positive conceivability – which will also play a crucial role later on.
Chalmers (2009) introduces some clarifications and emendations to this simple argument.
Chalmers employs the two dimensional semantic framework to characterize “primary possibility” and “secondary possibility” and argues for his Master Principle (MP) that conceivability implies primary possibility.19 The CP Principle (premise 2 of his argument) follows from this, on the plausible assumption that both P and Q express the same primary and secondary proposition. On the other hand, if we assume that P has different primary and secondary propositions, and assume that P&~Q is not possible, Russellian Monism follows.