In philosophy, mechanism is a theory that all natural phenomena can be explained by physical causes. It can be contrasted with vitalism, the philosophical theory that vital forces are active in living organisms, so that life cannot be explained solely by mechanism. 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.
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 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.
"I should like you to consider that these functions (including passion, memory, and imagination) follow from the mere arrangement of the machine’s organs every bit as naturally as the movements of a clock or other automaton follow from the arrangement of its counter-weights and wheels." (Descartes, Treatise on Man, p.108)
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 (electromagnetic) radiation are held to be at least coequal with "commonly understood" matter as constituents of the universe, and - possibly, under some interpretations - universal determinism is denied. (See quantum theory.) 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."
Universal mechanism has come and gone, but the debate over anthropic mechanism seems here to stay, at least for the time being. 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. In the first, 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 philosopher Paul Churchland. The second option, common 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.
Some scholars have debated over what, if anything, Gödel’s incompleteness theorems imply about anthropic mechanism. Much of the debate centers on whether the human mind is equivalent to a Turing machine, or by the Church-Turing thesis, any finite machine at all. If it is, and if the machine is consistent, then Gödel’s incompleteness theorems would apply to it.
One of the earliest attempts to use incompleteness to reason about human intelligence was by Gödel himself in his 1951 Gibbs lecture entitled "Some basic theorems on the foundations of mathematics and their philosophical implications". In this lecture, Gödel uses the incompleteness theorem to arrive at the following disjunction: (a) the human mind is not a consistent finite machine, or (b) there exist Diophantine equations for which it cannot decide whether solutions exist. Gödel finds (b) implausible, and thus seems to have believed the human mind was not equivalent to a finite machine, i.e., its power exceeded that of any finite machine. He recognized that this was only a conjecture, since one could never disprove (b). Yet he considered the disjunctive conclusion to be a "certain fact".
In subsequent years, more direct anti-mechanist lines of reasoning were apparently floating around the intellectual atmosphere. In 1960, Hilary Putnam published a paper entitled "Minds and Machines," in which he points out the flaws of a typical anti-mechanist argument. Informally, this is the argument that the (alleged) difference between "what can be mechanically proven" and "what can be seen to be true by humans" shows that human intelligence is not mechanical in nature. Or, as Putnam puts it:
Let T be a Turing machine which "represents" me in the sense that T can prove just the mathematical statements I prove. Then using Gödel’s technique I can discover a proposition that T cannot prove, and moreover I can prove this proposition. This refutes the assumption that T "represents" me, hence I am not a Turing machine.
Hilary Putnam objects that this argument ignores the issue of consistency. Gödel’s technique can only be applied to consistent systems. It is conceivable, argues Putnam, that the human mind is inconsistent. If one is to use Gödel’s technique to prove the proposition that T cannot prove, one must first prove (the mathematical statement representing) the consistency of T, a daunting and perhaps impossible task. Later Putnam suggested that while Gödel’s theorems cannot be applied to humans, since they make mistakes and are therefore inconsistent, it may be applied to the human faculty of science or mathematics in general. If we are to believe that it is consistent, then either we cannot prove its consistency, or it cannot be represented by a Turing machine.
J. R. Lucas in Minds, Machines and Gödel (1963), and later in his book The Freedom of the Will (1970), lays out an anti-mechanist argument closely following the one described by Putnam, including reasons for why the human mind can be considered consistent. Lucas admits that, by Gödel’s second theorem, a human mind cannot formally prove its own consistency, and even says (perhaps facetiously) that women and politicians are inconsistent. Nevertheless, he sets out arguments for why a male non-politician can be considered consistent. These arguments are philosophical in nature and are the subject of much debate; Lucas provides references to responses on his own website.
Another work was done by Judson Webb in his 1968 paper "Metamathematics and the Philosophy of Mind". Webb claims that previous attempts have glossed over whether one truly can see that the Gödelian statement p pertaining to oneself, is true. Using a different formulation of Gödel’s theorems, namely, that of Raymond Smullyan and Emil Post, Webb shows one can derive convincing arguments for oneself of both the truth and falsity of p. He furthermore argues that all arguments about the philosophical implications of Gödel’s theorems are really arguments about whether the Church-Turing thesis is true.
Later, Roger Penrose entered the fray, providing somewhat novel anti-mechanist arguments in his books, The Emperor’s New Mind(1989) [ENM] and Shadows of the Mind (1994) [SM]. These books have proved highly controversial. Martin Davis responded to ENM in his paper "Is Mathematical Insight Algorithmic?", where he argues that Penrose ignores the issue of consistency. Solomon Feferman gives a critical examination of SM in his paper "Penrose’s Gödelian argument".
One of the most lucid statements of a Godel based anti-mechanism argument can be found in Douglas Hofstatder’s Pulitzer Prize winning book, ’Godel, Escher, Bach: An Eternal Golden Braid’. This is particularly interesting, in that Hofstatder is widely viewed as one of the better known skeptics of such argument:
Looked at this way, Godel’s proof suggests -- though by no means does it prove! -- that there could be some high-level way of viewing the mind/brain, involving concepts which do not appear on lower levels, and that this level might have explanatory power that does not exist -- not even in principle -- on lower levels. It would mean that some facts could be explained on the high level quite easily, but not on lower levels at all. No matter how long and cumbersome a low-level statement were made, it would not explain the phenomena in question. It is analogous to the fact that, if you make derivation after derivation in [Peano arithmetic], no matter how long and cumbersome you make them, you will never come up with one for G -- despite the fact that on a higher level, you can see that [the Godel sentence] is true. What might such high-level concepts be? It has been proposed for eons, by various holistically or "soulistically" inclined scientists and humanists that consciousness is a phenomenon that escapes explanation in terms of brain components; so here is a candidate at least. There is also the ever-puzzling notion of free will. So perhaps these qualities could be "emergent" in the sense of requiring explanations which cannot be furnished by the physiology alone (’Godel, Escher, Bach’, p. 708).