Take a few bits of metal, work them into various shapes, and attach them to a piece of wood. Voila! A mousetrap. Or so we call it. But objectively, apart from human interests, the object is “nothing but” a collection of wood and metal parts. Its “mousetrappish” character is observer-relative; it is in the minds of the designer and users of the object, and not strictly in the object itself. “Reductionism” with respect to such human artifacts is just common sense. We know that cars, computers, and cakes are objectively “nothing but” the parts that make them up – that their “carlike,” “computerlike,” or “cakelike” qualities are not really there inherently in the parts, but are observer-relative – precisely because we took the parts and rearranged them to perform a function we want them to perform but which they have no tendency to perform on their own.
But now consider claims like “Consciousness is ‘nothing but’ a complex set of electrochemical processes in the brain,”“Living things are ‘nothing but’ aggregates of physico-chemical processes,” “Water is ‘nothing but’ H2O,” and so forth. Claims like these – indeed, reductionism about natural kinds in general – are, I think it will generally be acknowledged, not in line with common sense. For the Aristotelian-Thomistic (A-T) metaphysician, they are not true either – not even the claim about water. “H20” abbreviates a description of the chemical micro-structure of water, but for A-T essentialism, macro-level substances are not reducible to their micro-structure. (See the relevant sections of Oderberg’s Real Essentialism for a useful discussion.) A-T analysis is holistic rather than reductionist; a whole can be analyzed into its parts, but the parts in turn cannot properly be understood apart from the whole. And the end-directedness characteristic of natural substances – conscious purposes in the case of human beings, biological functions in the case of living things in general, causal tendencies in the case of inorganic phenomena no less than organic ones – is inherent to them rather than observer-relative or imposed from outside, and irreducible to patterns of efficient causation.
But leave all that aside; obviously, the A-T view is controversial. The point for now is that, to make reductionism about natural kinds plausible, one must substitute for common sense some alternative picture of the natural world – in particular, a picture on which every feature of a natural substance is either entirely definable in terms of the features of its parts or can be interpreted as observer-relative. That is to say, one must substitute for common sense the idea that a natural substance is a kind of artifact. One must think of plants and animals, solar systems and galaxies, as comparable to (say) mousetraps, watches, or outboard motors.
And that is, of course, exactly what the “mechanical” conception of the world that the early modern philosophers put in place of the Scholastics’ Aristotelian philosophy of nature made possible. The world was reconceived as a machine or collection of machines. Break a natural object down into its parts and identify the efficient-causal relations holding between them, and you know (so the moderns claim) everything there is to know about its intrinsic nature. Anything irreducible to this – such as final causality or end-directedness, or a “formal cause” over and above the sum of the parts – is extrinsic to it, observer-relative, whether the observer is a human being or a divine artificer. For Aristotle, “art imitates nature” – that is to say, artifacts copy nature’s way of doing things, but only (of course) artificially since their parts have no inherenttendency to do what we make them do. The moderns reverse this – nature is for them a kind of “art,” in the sense that natural objects are to be modeled on artifacts rather than the other way around.
Early modern thinkers like Descartes, Newton, Boyle, and Locke were quite happy to associate a “machinist” with the “machines” they saw in the natural world. Hence they did not deny that things had final causes of some sort, since God had made them for a purpose. But the purposes were now as extrinsic to natural objects as the mousetrap’s purpose is extrinsic to the wood and metal that make it up, residing entirely in the mind of the divine artificer and in no sense in the things themselves; and for Descartes, these purposes are therefore as inscrutable as the divine will is. (For a useful brief account of the transition from the Aristotelian-Scholastic conception of purpose in nature to the modern “mechanistic” conception, see Margaret Osler’s paper “From Immanent Natures to Nature as Artifice: The Reinterpretation of Final Causes in Seventeenth-Century Natural Philosophy,” The Monist vol. 79, no. 3.)
It was bound to occur to someone that if the world is a kind of machine or artifact, it might carry on in existence in the absence of the machinist or artificer, just as human artifacts do. Now, given A-T metaphysics, such a “world without God” is impossible in principle. To be sure, a natural substance’s final cause is inherent to it, something it cannot fail to have given its nature or essence; and that entails (contra Descartes) that we can know a thing’s nature and final cause without adverting directly to God’s intentions. But this does not entail that a thing could exist, even for an instant, apart from God. That the prime matter (or “pure potency”) that underlies the natural world is actualized in just the way it is at any given moment requires a “purely actual” Unmoved Mover; that a thing’s nature or essence is conjoined at any instant with an “act of existing” requires an Uncaused Cause that is ipsum esse subsistens. (See Aquinasfor the full story.) But when these Scholastic metaphysical underpinnings of natural theology were pushed aside in favor of the “mechanical” conception of the world, the stage was set for deism.
The sequel, naturally, was atheism. For if the “machine” can exist nowwithout a “machinist,” maybe it has always existed without him. Maybe the machine is all that ever existed in the first place. The only question remaining is whether this is “probable,” whether it is the “best explanation” of the “empirical evidence”; and the metaphysically unavoidable God of classical theism is transformed thereby into the “scientific hypothesis” of William Paley and “Intelligent Design” theory.
More to the present point, the way was also opened to the ever more radical forms of reductionism and eliminativism that have characterized modern philosophy. If formal and final causes – Aristotelian essences or natures, and natural ends or purposes – do not exist either inherent in nature itself or in the mind of a divine artificer, the only thing left for them to be are projections of the human mind. There is at least constant pressure, given the mechanistic model of the natural world shared by modern dualists and materialists, modern theists and atheists alike, to regard natural substances as “nothing but” material parts related by patterns of efficient causality.
The results are often absurd and even morally obscene, though modern philosophers have found themselves increasingly happy to live with that. But the mechanistic conception of nature that leads to reductionism and eliminativism is in any event incoherent. For the mind that does the “projecting” in question cannot itself coherently be either reduced or eliminated (as Cartesian mechanists realize, which makes their position at least more sane than that of the materialist); and (as Cartesian mechanists do not realize any more than materialists do) the efficient causality the whole mechanistic model presupposes ultimately cannot be made sense of apart from something like the substantial forms and final causality the mechanist eschews. (See The Last Superstition for the full story.)
Into the bargain, the whole picture gives rise, when not taken in an atheistic direction, to a theology that is difficult or impossible to reconcile with the classical theism at the core of historical Christianity. And that is why A-T philosophers are often so critical of Paley-style “design arguments” and of ID theory – a subject I have addressed in several places, including here and here. (Since certain readers seem hell bent on missing the point, let me repeat a couple of things I’ve said many times already. The A-T critique of Paley and of ID theory has nothing whatsoever to do with Darwinism – Aristotle and Aquinas were not Darwinians, after all – and it has nothing to do either with any objection to probabilistic arguments for God’s existence per se. It has to do instead with the metaphysical and theological errors A-T sees as implicit in the methodological assumptions underlying Paley’s “design argument” and contemporary ID theory.)
In short, while the “world as artifact” model the early modern philosophers put at the center of Western thought was regarded by many of them as a means of defending the religious and moral heritage of the West, it was in fact quite the opposite. In reality it was, and is – if I may wax Marxian – the “objective ally” of deism, atheism, and reductionism. Hence it is simply not to the point to debate with Darwinians whether or not the cosmic watchmaker is “blind” (as Richard Dawkins would put it). The fundamental error – made by Darwinian naturalists and ID theorists alike – is to think of the world as a “watch” in the first place.