- We are all physicalists now. It was not always so. A hundred years ago most educated thinkers had no doubt that non-physical processes occurred within living bodies and intelligent minds. Nor was this an anti-scientific stance: the point would have been happily agreed by most practicing scientists of the time. Yet nowadays anybody who says that minds and bodies involve non-physical processes is regarded as a crank1. This is a profound intellectual shift. In this essay I want to explore its methodological implications for the human sciences. I do not think that these have been adequately appreciated.
- It is sometimes suggested that the modern enthusiasm for physicalism is some kind of intellectual fad, fanned by the great successes of physical science during the twentieth century. But this underestimates the underpinnings of contemporary physicalism. The reason that scientists a hundred years ago were happy to countenance non-physical processes is that nothing in the basic principles of mechanics ruled them out. Mechanics tells us how material bodies respond to forces, but says little about what forces exist. Prior to the twentieth century, orthodox scientists countenanced a far wider range of independent forces than are admitted today: these included not only separate chemical, cohesive, and frictional forces, but also special vital and nervous forces. (Consider the term ‘nervous energy’. This was originally a nineteenth-century term for the potential energy of the nervous force field. Nervous energy was supposed to be stored up during cognition and then converted into the kinetic energy during action.)
- The verdict of the twentieth century, however, has been that there are no such special forces. A great deal of detailed experimental research, including detailed physiological research into the internal working of living cells, has failed to uncover any evidence of material processes that cannot be accounted for by a few fundamental forces (gravity, electromagnetism, the strong and weak nuclear forces). Because of this, special vital or mental forces are now discredited, along with chemical, cohesive, and frictional forces. The basic physical forces are almost universally regarded as adequate to account for all material processes. (For the history of physicalism, see "Papineau (David) - Thinking About Consciousness", 2002, Appendix2.)
- Where does this leave thoughts, feelings, relationships, institutions and the other familiar human entities that form the subject matter of the human sciences? At first sight it might seem that they must be dismissed as illusory. If all material effects are due to purely physical influences, then doesn’t this show that the putative components of human reality don’t make a difference to anything? But this would be too quick. Perhaps these human components are themselves part of the physical world, and so perfectly able to influence material processes. This is the reductionist3 option. We don’t take the advances of physical science to show there are no thoughts or institutions. Rather, we conclude that thoughts and institutions are themselves physical entities, and so perfectly real. (Compare the way that heat was reduced by the kinetic theory of gases4, rather than eliminated. The kinetic theory showed that all the supposed effects of heat can be explained by the motion of molecules. But science didn’t conclude that therefore there is no heat. Rather it said that heat is nothing more than molecular motion.)
- This reductionist option promises to save the subject matter of the human sciences. But at the same time it threatens their autonomy. Before the rise of physicalism, the human sciences could regard themselves as identifying mental, behavioural and social patterns that were separate from any physical principles. Of course, such human processes could have effects in the material world, just as Descartes’ immaterial mind could have effects on the body. But these human processes would not themselves be part of the physical world, and so would not be governed by physical principles. Mental, behavioural and social patterns would be quite independent of the laws of physics.
- However, this autonomy is threatened by physicalism. According to Ernest Nagel’s classic model of reduction5 (19616), any patterns displayed at the level of a ‘reduced’ science are special cases of the laws of the ‘reducing’ sciences. On Nagel’s conception, reduction requires the categories of the reduced science to be identified with categories of the reducing science, via ‘bridge laws’. In consequence, any regularities of the reduced science can in principle be rewritten as regularities of the reducing science. In the kind of case we are interested in, this would mean psychological, economic and other human categories must be specifiable in purely physical terms, and that any laws involving these categories must be expressible as purely physical laws.
- In due course we shall consider further how far this classical reductionist model really does impugn the autonomy of the human sciences. But first we need to consider whether classical reduction is really forced on us by physicalism. This would be denied by many philosophers today. Over the past fifty years, philosophers have devoted a great deal of energy to developing varieties of ‘non-reductive physicalism7’. The idea here is to go along with the basic physicalist thought that human entities must be physical if they are to make a difference in the real world, but to deny that the specific requirements of classic Nagelian reduction follow. (The terminology can be a bit confusing here. By ordinary standards, ‘non-reductive physicalism’ would be counted as a species of reductionism, since it rejects any ontological pluralism and collapses all reality, including human reality, into the physical realm. But in this paper I shall adhere to contemporary philosophical jargon, reserving ‘reductionism8’ for the stronger requirements of Nagel’s classic model, and using ‘physicalism9’ for the more general denial of ontological pluralism10.)
Footnote 1: Footnote 2: Footnote 4:
- This seems to be the “poster boy” of Reductionism. It’d be nice to see other examples.
- Also, it’s only heat in certain circumstances that’s so reduced. Gaseous plasmas are hot, but don’t have any molecules.
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