Wholes and parts

Sensible qualities are not primary: colour, heat, taste, even life and sensation, arise from the arrangement, motion and collisions of atoms that themselves have neither colour nor heat. The whole therefore adds nothing to its parts: it is only atoms variously disposed, and it is their configuration that explains the world's variety. This bottom-up explanation, in which the higher reduces entirely to the meeting of the smallest, is a reductionism that continues the line of Democritus.

On the Nature of Things, II, 730-864 (atoms are colourless; colour arises from their arrangement) · On the Nature of Things, II, 865-990 (the sentient arises from the non-sentient)

The living body, the human body included, is fully explained as a machine: circulation, digestion, and the motion of the limbs reduce to the sole laws of shape and motion, with no superadded vital principle required. Life is reduced to mechanism, the soul belonging to another order entirely.

Discourse on Method, V · Treatise on Man

The rule of method is explicit, and Russell holds it to be the supreme maxim of philosophical work: wherever possible, substitute constructions out of known entities for inferences to unknown entities. It is reductionist out of economy rather than materialism: a point of space, an instant, a physical object, a person, a number all become classes or series of already admitted elements, and whatever cannot be built that way is to be suspected. The reduction aimed at is logical, not physical: Russell does not reduce mind to matter, he reduces both to groupings of events.

"Logical Atomism" (1924) · Our Knowledge of the External World (1914) · Introduction to Mathematical Philosophy (1919)

Smart holds that an explanation is complete only when carried back to physical constituents and their interactions. Admitting properties that would escape this analysis would force supernumerary laws, with no role in the edifice of science, which a principle of economy forbids. His identity theory applies this reductionism to mind: not one more property arising from the brain, but the same processes, described in another vocabulary.

Philosophy and Scientific Realism (1963)

Dennett defends explanation by parts while refusing its caricature. He coins the phrase greedy reductionism for the haste to skip intermediate levels, to explain mind by neurons without passing through the processing mechanisms that do the work. Good reductionism keeps the storeys: it shows how, degree by degree, processes devoid of intelligence end up producing competence, without ever adding anything to matter.

Darwin's Dangerous Idea (1995)

Strawson does not refuse every emergence: the liquidity of water is perfectly intelligible from the behaviour of molecules, and that is the model of what he accepts. What he rejects is brute emergence, that of a radically new property arising from constituents bearing no trace of it: whatever emerges must be intelligible from that out of which it emerges. Applied to experience, this refusal leads him not to classical reductionism but to panpsychism: if lived experience cannot arise from what contains none of it, then it was already there.

"Realistic Monism" (2006)

Chalmers distinguishes two emergences. Weak emergence covers phenomena one would not have guessed from the parts, but which follow from them once one knows where to look, like the patterns of a cellular automaton. Strong emergence is that of a property deducible from no knowledge of the parts, however complete, and he takes consciousness to be its only uncontestable case in nature. Hence his conclusion: psychophysical laws must be added to the inventory of the world, as physics had to add electromagnetism to mechanics.

"Strong and Weak Emergence" (2006)

Nagel disputes that analysis into physical constituents can exhaust everything. How does matter produce conscious beings? A successful explanation of life and mind would have to make it intelligible that matter produces conscious beings; yet describing the parts and their interactions leaves precisely that unexplained. His anti-reductionism therefore calls for principles of another order, without his claiming to have found them. The hypothesis of a natural teleology he then advances, offering it as speculative, has been widely rejected, including by readers who share his refusal of reductionism.

The View from Nowhere (1986) · Mind and Cosmos (2012)

Searle holds consciousness to be a higher-level property caused by neuronal processes, as the liquidity of water is caused by the behaviour of molecules although no molecule is liquid. The emergence he accepts is that one: explicable from the parts once their organization is known. He refuses, by contrast, any property that would possess causal powers inexplicable from the elements, which would amount, he says, to magic. He therefore sits barely on the emergentist side, and not at all on the side of a mysterious whole.

The Rediscovery of the Mind (1992)