For SIFA conference, Vietri sul Mare, October 2003
Physicalism as emergence
Tim Crane, UCL
- Introduction
Rough definitions: The physical = the subject-matter of physics; a physical thing = an entity (object, property etc.) which is postulated by physics, the subject-matter of some physical theory; Physicalism = the thesis that in some sense everything is physical.
But in what sense? A dilemma:
Strong sense: ‘Only physical things exist’.
Weak sense: ‘Everything is either a physical thing or has some physical properties’.
Aim of this paper: to argue that (a) there is no viable and interestingly physicalist position lying between the horns of this dilemma; and that (b) this is the proper lesson of two well-known arguments against physicalism.
- Two kinds of reduction
Physicalism is often called a reductive view; but what does this mean? A basic distinction:
(OR) Ontological reduction = ‘reduction’ of entities; the identification of a class of entities as a sub-class of another (e.g. the Lewis-Armstrong identity theory of mind).
(ER) Explanatory reduction = ‘reduction’ of facts or theories; the explanation of one fact or theory in terms of another.
These kinds of reduction are independent of one another (cf. Davidson 1970 and Block 1997).
- The supposed distinction between physicalism and emergence
An ontological reduction of the mental to the physical is sufficient for physicalism, since it identifies mental and physical phenomena, and can therefore assert ‘everything is physical’ in the strong sense (§1).
But is it necessary? Not according to non-reductive physicalism, which holds that:
(A) all objects have some physical properties;
(B) not all properties are physical;
(C) everything supervenes upon the physical.
But these three claims are accepted by a traditional emergentist too (e.g. Broad 1929; McLaughlin 1992). So how then should physicalism be distinguished from emergentism, the view that mental properties ‘emerge’ from the physical? Terence Horgan (1993: 560) has the answer:
‘A physicalist position should surely assert, contrary to emergentism, (i) that physics is causally complete (i.e. all fundamental causal forces are physical forces, and the laws of physics are never violated); and (ii) that any metaphysically basic facts or laws—any unexplained explainers, so to speak—are facts or laws within physics itself.’
What is essential to physicalism, on this view, is not necessarily the number of things it says there are, but how they are (explanatorily) related. So physicalism must accept either an ontological reduction or an explanatory reduction, or both. There thus seem to be three varieties of physicalism: OR physicalism, OR+ER physicalism and ER physicalism. Jackson’s (1998) popular definition of physicalism – ‘any world which is a minimal physical duplicate of the actual world is a duplicate simpliciter’ – is compatible with all these varieties of physicalism, and does not distinguish between them. (Although Jackson’s independent claim that physicalism requires the a priori deducibility of the mental facts from the physical facts is a form of ER physicalism.)
OR physicalism is either eliminative (e.g. Quine) about non-physical categories, or not. The main obstacle with the non-eliminative version of OR is the variable/multiple realisation. (‘For nearly thirty years, there has been a consensus (at least in English-speaking countries) that reductionism is a mistake and that there are autonomous special sciences. This consensus has been based on an argument from multiple realizability.’ Block 1997:107.) But what about the other, more general, objections to physicalism?
- Two arguments against (some form of) physicalism
The Knowledge Argument (Russell 1927; Broad 1929; Feigl 1958; Jackson 1982; Robinson 1982): an omniscient colour scientist lives the black-and-white-room, then sees red for the first time; she learns something new. She knew all the physical facts before seeing red, so what she learns when she sees red is not a physical fact; therefore not all facts are physical facts.
The Explanatory Gap (Levine 2001): Even if the mental is physical, there is no deduction of the facts about consciousness from the physical facts, and hence no explanation of consciousness.
- How should a physicalist respond to these two arguments?
Many physicalists (e.g. Horgan 1984, Papineau 2002)have argued that these arguments do not touch an OR physicalist position. They are right. So if these arguments work at all, they challenge ER physicalism.
The most plausible physicalist response to the Knowledge Argument is to accept that the argument is sound, but to deny that physicalism requires that all facts (truths) be expressible in the language of physics. If this is true, then there are facts that have no physical explanation. But then there must be an explanatory gap of some kind. So if an ER physicalist wants to close the explanatory gap, then they cannot give this (independently plausible) response to the Knowledge Argument.
If someone wants to give this most plausible response to the knowledge argument, and hold onto (A), (B) and (C) (see §3), then they must abandon ER.
- Non-OR physicalism as emergence?
OR physicalism is distinct from emergence; but ER physicalism falls victim to the best understanding of the Knowledge Argument. If the Knowledge Argument works, then someone who holds (A), (B) and (C) should really then be an emergentist. The most plausible form of non-reductive physicalism is really emergentism.
Given the cogency of the Knowledge Argument, there is no room for a physicalist position which denies ontological reduction and accepts explanatory reduction. This is the proper lesson of these arguments against physicalism.
REFERENCES
Block, Ned, 1997, ‘Anti-reductionism Slaps Back’ Mind, Causation, World, Philosophical Perspectives 11: 107-133.
Broad, C.D., 1926, The Mind and its Place in Nature (Routledge and Kegan Paul).
Davidson, Donald, 1970, ‘Mental Events’ in Essays on Actions and Events (Oxford University Press 1980).
Feigl, H., 1958, The ‘Mental’ and the ‘Physical’ (University of Minnesota Press).
Horgan, Terrence, 1984,‘Jackson on Physical Information and Qualia’ Philosophical Quarterly 34: 147-152
Horgan, Terence, 1993, From supervenience to superdupervenience: meeting the demands of a material world Mind 102: 555-586.
Jackson, Frank, 1982, ‘Epiphenomenal Qualia’ Philosophical Quarterly 32 (1982) 127-36.
Jackson, Frank, 1998, From Metaphysics to Ethics (Oxford University Press).
Levine, Joseph, 2001, Purple Haze(Oxford University Press).
McLaughlin, Brian, 1992, ‘The Rise and Fall of British Emergentism’ in Emergence or Reduction? A. Beckermann et al (eds.) (De Gruyter).
Papineau, David, 2002, Thinking About Consciousness (Oxford University Press).
Robinson, Howard, 1982, Matter and Sense (Cambridge University Press)
Russell, Bertrand, 1927, The Analysis of Matter (George Allen and Unwin)