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Mechanism (philosophy)

The doctrine of mechanism in philosophy comes in two different flavors. They are both doctrines of metaphysics, but they are different in scope and ambitions: the first is a global doctrine about nature, which has been more or less thoroughly abandoned; the second is a local doctrine about human beings and their minds, which is hotly contested. For clarity we might distinguish these two doctrines as universal mechanism and anthropic mechanism.

Universal mechanism

The older doctrine which we have called universal mechanism is a theory about the nature of the universe, closely linked with the early modern version of materialism. Universal mechanism held that the universe is best understood as a completely mechanical system--that is, a system composed entirely of matter in motion under a complete and regular system of laws of nature. The mechanists understood the achievements of the Scientific Revolution to show that every phenomenon in the universe could eventually be explained in terms of mechanical laws: that is, in terms of natural laws governing the motion and collision of matter. It follows that mechanism is a form of thoroughgoing determinism: if all phenomena can be explained entirely through the motion of matter under physical laws, then just as surely as the gears of a clock completely determine that it will strike 2:00 an hour after it strikes 1:00, all phenomena are completely determined by the properties of that matter and the operations of those natural laws. (Indeed, the determinism implied by universal mechanism is even stronger than clockwork: whereas the mechanism of a clock may cease to work predictably as its parts break down, the "parts" of the system in universal mechanism are nothing less than everything in the universe — anything that they "broke down" into would still be a part of the universe, and so would still be subject to the mechanistic laws of nature. The French mechanist and determinist Pierre Simon de Laplace memorably formulated the sweeping implications of this thesis by saying:

"We may regard the present state of the universe as the effect of the past and the cause of the future. An intellect which at any given moment knew all of the forces that animate nature and the mutual positions of the beings that compose it, if this intellect were vast enough to submit the data to analysis, could condense into a single formula the movement of the greatest bodies of the universe and that of the lightest atom; for such an intellect nothing could be uncertain and the future just like the past would be present before its eyes."

One of the first and most famous expositions of universal mechanism is found in the opening passages of the Leviathan by Thomas Hobbes (1651). What is less frequently appreciated is that René Descartes, who is today remembered mainly as a paradigmatic enemy of materialism and mechanism (and in that respect quite the opposite of Hobbes), also did much to advance the mechanistic understanding of nature, in both his scientific works on mechanics and in his philosophical works on metaphysics. Descartes was a substance dualist, and argued that reality was composed of two radically different types of substance: corporeal substance, on the one hand, and mental substance, on the other hand. Descartes steadfastly denied that the human mind could be explained in terms of the configurations of corporeal substance (a chief claim of all forms of mechanism). Nevertheless, his understanding of corporeal substance was thoroughly mechanistic; his scientific work was based on the understanding of all natural objects, including not only billiard balls and rocks, but also non-human animals and even human bodies, as completely mechanistic automata. Descartes' dualism was, in no small part, motivated by the fact that he could see no place for the soul or for freedom of the will in his thoroughly mechanistic understanding of nature. Ancient naturalists such as Aristotle, on the other hand, had no need for substance dualism because their conception of nature was teleological rather than mechanistic, and was compatible with a robust sense of human freedom. Descartes, then, can be seen as agreeing with the early modern mechanists, and disagreeing with Aristotle, on the nature of the physical world. The difference between Descartes and his mechanist colleagues was that mechanists either saw no problem for the notions of soul and freedom of the will, or else were simply willing to dispense with these notions altogether.

The mechanistic worldview gained considerable favor with the revolutionary successes of Isaac Newton, whose work in mechanics seemed to successfully explain the motion of everything in heaven and in earth according to the operation of a single mechanical principle. To be sure, that principle — universal gravitation — was something of a disappointment to the older cadre of mechanists, since mechanism originally sought to explain all phenomena entirely in terms of the motion and collision of material bodies, whereas Newton's principle of gravitation required action at a distance. Nevertheless, the generation of philosophers who were inspired by Newton's example carried the mechanist banner. Chief among them were French philosophes such as Julien Offray de La Mettrie and Denis Diderot (see also: French materialism).

Universal mechanism has since fallen into disfavor - not so much because philosophers are less inclined toward a scientific worldview now than they were in the 17th and 18th centuries, but rather because physical science has abandoned the mechanistic worldview in favor of one in which phenomena such as energy are held to be at least coequal with matter as constituents of the universe, and — possibly, under some interpretations — universal determinism is denied. The motivations that led some philosophers to mechanism in the 17th and 18th centuries now lead philosophers of a similar temperament towards physicalism, which leaves the specification of the primitive contents of the universe to a "completed physics."

Anthropic mechanism

Universal mechanism has come and gone, but the debate over anthropic mechanism seems here to stay. The thesis in anthropic mechanism is not that the everything can be completely explained in mechanical terms (although some anthropic mechanists may also believe that), but rather that everything about human beings can be completely explained in mechanical terms, as surely as can everything about clockwork or gasoline engines.

One of the chief obstacles that all mechanistic theories have faced is providing a mechanistic explanation of the human mind; Descartes, for one, endorsed dualism in spite of endorsing a completely mechanistic conception of the material world because he argued that mechanism and the notion of a mind were logically incompatible. Hobbes, on the other hand, conceived of the mind and the will as purely mechanistic, completely explicable in terms of the effects of perception and the pursuit of desire, which in turn he held to be completely explicable in terms of the materialistic operations of the nervous system. Following Hobbes, other mechanists argued for a thoroughly mechanistic explanation of the mind, with one of the most influential and controversial expositions of the doctrine being offered by Julien Offray de La Mettrie in his Man a Machine (1748).

Today, as in the past, the main points of debate between anthropic mechanists and anti-mechanists is mainly occupied with two topics: the mind — and consciousness, in particular — and free will. Anti-mechanists argue that anthropic mechanism is incompatible with our commonsense intuitions: in philosophy of mind they argue that unconscious matter cannot completely explain the phenomenon of consciousness, and in metaphysics they argue that anthropic mechanism implies determinism about human action, which (they argue) is incompatible with our understanding of ourselves as creatures with free will. In order to hold on to the ways in which we understand ourselves, they argue, we are logically committed to rejecting mechanism. Contemporary philosophers who have argued for this position include Norman Malcolm and David Chalmers.

Anthropic mechanists typically respond in one of two ways: either they dig in or they try to find a way to finesse the problem. In the former case, they agree with anti-mechanists that mechanism conflicts with some of our commonsense intuitions, but go on to argue that our commonsense intuitions are simply mistaken and need to be revised. Down this path lie eliminative materialism in philosophy of mind, and hard determinism on the question of free will. This option is popular with some scientists, but it is rejected by most philosophers. (Although not by its most well-known advocate, the eliminative materialist Paul Churchland. The more common option, amongst philosophers who adopt anthropic mechanism, is to argue that the arguments given for incompatibility are specious: whatever it is we mean by "consciousness" and "free will," they urge, it is fully compatible with a mechanistic understanding of the human mind and will. As a result they tend to argue for one or another non-eliminativist physicalist theories of mind, and for compatibilism on the question of free will. Contemporary philosophers who have argued for this sort of account include J. J. C. Smart and Daniel Dennett.