Eliminative materialism
Eliminative materialism (also called eliminativism) is a materialist position in the philosophy of mind. It is the idea that the majority of mental states in folk psychology do not exist.[1] Some supporters of eliminativism argue that no coherent neural basis will be found for many everyday psychological concepts such as belief or desire, since they are poorly defined. The argument is that psychological concepts of behavior and experience should be judged by how well they reduce to the biological level.[2] Other versions entail the nonexistence of conscious mental states such as pain and visual perceptions.[3]
Eliminativism about a class of entities is the view that the class of entities does not exist.[4] For example, materialism tends to be eliminativist about the soul; modern chemists are eliminativist about phlogiston; modern biologists are eliminativist about élan vital; and modern physicists are eliminativist about luminiferous ether. Eliminative materialism is the relatively new (1960s–70s) idea that certain classes of mental entities that common sense takes for granted, such as beliefs, desires, and the subjective sensation of pain, do not exist.[5][6] The most common versions are eliminativism about propositional attitudes, as expressed by Paul and Patricia Churchland,[7] and eliminativism about qualia (subjective interpretations about particular instances of subjective experience), as expressed by Daniel Dennett, Georges Rey,[3] and Jacy Reese Anthis.[8]
In the context of materialist understandings of psychology, eliminativism is the opposite of reductive materialism, arguing that mental states as conventionally understood do exist, and directly correspond to the physical state of the nervous system.[9] An intermediate position, revisionary materialism, often argues the mental state in question will prove to be somewhat reducible to physical phenomena—with some changes needed to the commonsense concept.[1][10]
Since eliminative materialism arguably claims that future research will fail to find a neuronal basis for various mental phenomena, it may need to wait for science to progress further. One might question the position on these grounds, but philosophers like Churchland argue that eliminativism is often necessary in order to open the minds of thinkers to new evidence and better explanations.[9] Views closely related to eliminativism include illusionism and quietism.
Arguments for eliminativism[edit]
Problems with folk theories[edit]
Eliminativists such as Paul and Patricia Churchland argue that folk psychology is a fully developed but non-formalized theory of human behavior. It is used to explain and make predictions about human mental states and behavior. This view is often referred to as the theory of mind or just simply theory-theory, for it theorizes the existence of an unacknowledged theory. As a theory in the scientific sense, eliminativists maintain, folk psychology must be evaluated on the basis of its predictive power and explanatory success as a research program for the investigation of the mind/brain.[31][32]
Such eliminativists have developed different arguments to show that folk psychology is a seriously mistaken theory and should be abolished. They argue that folk psychology excludes from its purview or has traditionally been mistaken about many important mental phenomena that can and are being examined and explained by modern neuroscience. Some examples are dreaming, consciousness, mental disorders, learning processes, and memory abilities. Furthermore, they argue, folk psychology's development in the last 2,500 years has not been significant and it is therefore stagnant. The ancient Greeks already had a folk psychology comparable to modern views. But in contrast to this lack of development, neuroscience is rapidly progressing and, in their view, can explain many cognitive processes that folk psychology cannot.[22][33]
Folk psychology retains characteristics of now obsolete theories or legends from the past. Ancient societies tried to explain the physical mysteries of nature by ascribing mental conditions to them in such statements as "the sea is angry". Gradually, these everyday folk psychological explanations were replaced by more efficient scientific descriptions. Today, eliminativists argue, there is no reason not to accept an effective scientific account of cognition. If such an explanation existed, then there would be no need for folk-psychological explanations of behavior, and the latter would be eliminated the same way as the mythological explanations the ancients used.[34]
Another line of argument is the meta-induction based on what eliminativists view as the disastrous historical record of folk theories in general. Ancient pre-scientific "theories" of folk biology, folk physics, and folk cosmology have all proven radically wrong. Eliminativists argue the same in the case of folk psychology. There seems no logical basis, to the eliminativist, to make an exception just because folk psychology has lasted longer and is more intuitive or instinctively plausible than other folk theories.[33] Indeed, the eliminativists warn, considerations of intuitive plausibility may be precisely the result of the deeply entrenched nature in society of folk psychology itself. It may be that people's beliefs and other such states are as theory-laden as external perceptions and hence that intuitions will tend to be biased in their favor.[23]
Specific problems with folk psychology[edit]
Much of folk psychology involves the attribution of intentional states (or more specifically as a subclass, propositional attitudes). Eliminativists point out that these states are generally ascribed syntactic and semantic properties. An example of this is the language of thought hypothesis, which attributes a discrete, combinatorial syntax and other linguistic properties to these mental phenomena. Eliminativists argue that such discrete, combinatorial characteristics have no place in neuroscience, which speaks of action potentials, spiking frequencies, and other continuous and distributed effects. Hence, the syntactic structures assumed by folk psychology have no place in such a structure as the brain.[22] To this there have been two responses. On the one hand, some philosophers deny that mental states are linguistic and see this as a straw man argument.[35][36] The other view is represented by those who subscribe to "a language of thought". They assert that mental states can be multiply realized and that functional characterizations are just higher-level characterizations of what happens at the physical level.[37][38]
It has also been argued against folk psychology that the intentionality of mental states like belief implies that they have semantic qualities. Specifically, their meaning is determined by the things they are about in the external world. This makes it difficult to explain how they can play the causal roles they are supposed to in cognitive processes.[39]
In recent years, this latter argument has been fortified by the theory of connectionism. Many connectionist models of the brain have been developed in which the processes of language learning and other forms of representation are highly distributed and parallel. This tends to indicate that such discrete and semantically endowed entities as beliefs and desires are unnecessary.[40]
Evolution eliminates intentionality[edit]
Any naturalistic, purely causal, non-semantic account of content must rely on Darwinian natural selection to build neural states capable of storing unique propositions, as required by folk psychology. Theories that attempt to account for intentionality within materialism face the disjunction problem, which results in the indeterminacy of propositional content. If such theories cannot solve the disjunction problem, then neurons cannot store unique propositions. The only process that can build neural circuits, evolution by natural selection, cannot solve the disjunction problem. The whole point of Darwin's theory is that in the creation of adaptations, nature is not active but passive. What is really going on is environmental filtration—a purely passive and not very discriminating process that prevents most traits below some minimal local threshold from persisting. Natural selection is selection against. Selection for requires foresight, planning, and purpose. Darwin's achievement was to show that the appearance of purpose belies the reality of purposeless, unforesighted, unplanned, mindless causation. All adaptation requires is selection against. That was Darwin's point. But the combination of blind variation and selection against is not possible without disjunctive outcomes.[41][42][43]
It is important that selection against is not the contradictory of selection for, i.e. that selection against trait T is not just selection for trait not-T. This is because there are traits that are neither selected against nor selected for: the neutral ones that biologists, especially molecular evolutionary biologists, call silent, switched off, junk, non-coding, etc. Selection for and selection against are contraries, not contradictories.[41][42]
Natural selection cannot discriminate between coextensive properties. To see how Darwinian selection against works in a real case, consider two distinct gene products, one of which is neutral or even harmful to an organism and the other of which is beneficial, that are coded for by adjacent genes on the chromosomes. This is the phenomenon of genetic linkage. The traits that the genes coded for will be coextensive in a population because the gene-types are coextensive in that population. Mendelian assortment and segregation do not break up these packages of genes with any efficiency. Only crossover, the breaking up and faulty re-annealing of chromosomal strings or similar processes, can do this. As Darwin realized, no process producing variants in nature picks up on future usefulness, convenience, need, or adaptational value. The only thing evolution (natural selection-against) can do about the free-riding maladaptive or neutral trait, whose genes are riding along close to the genes for an adaptive trait, is wait around for the genetic material to be broken at just the right place, between the genes. Once this happens, Darwinian processes can begin to tell the difference between them. But only when environmental vicissitudes break up the DNA on which the two adjacent genes sit can selection against get started—if one of the two proteins is harmful.[41][42]
Darwinian theory's disjunction problem is that the process Darwin discovered cannot tell the difference between these two genes or their traits until crossover breaks the linkage between one gene, which is going to increase its frequency, and the other, which is going to decrease its frequency. If they are never separated, it will remain blind to their differences forever. What is worse, and more likely, one gene sequence can code for a favorable trait—a protein required for survival—while part of the same sequence can code for a maladaptive trait—some gene product that reduces fitness. Natural selection will have an even harder time discriminating between these two traits. Since evolution cannot solve the disjunction problem, the right conclusion for the materialist is to accept eliminativism by denying that neural states have as their informational content specific, particular, determinate statements that attribute non-disjunctive properties and relations to non-disjunctive subjects.[41][42][44][45][46]
Arguments against eliminativism[edit]
Intentionality and consciousness are identical[edit]
Some eliminativists reject intentionality while accepting the existence of qualia. Other eliminativists reject qualia while accepting intentionality. Many philosophers argue that intentionality cannot exist without consciousness and vice versa, and so any philosopher who accepts one while rejecting the other is being inconsistent. They argue that, to be consistent, one must accept both qualia and intentionality or reject them both. Philosophers who argue for such a position include Philip Goff, Terence Horgan, Uriah Kriegal, and John Tienson.[47][48] The philosopher Keith Frankish accepts the existence of intentionality but holds to illusionism about consciousness because he rejects qualia. Goff notes that beliefs are a kind of propositional thought.
Intuitive reservations[edit]
The thesis of eliminativism seems so obviously wrong to many critics, who find it undeniable that people know immediately and indubitably that they have minds, that argumentation seems unnecessary. This sort of intuition-pumping is illustrated by asking what happens when one asks oneself honestly if one has mental states.[49] Eliminativists object to such a rebuttal of their position by claiming that intuitions often are mistaken. Analogies from the history of science are frequently invoked to buttress this observation: it may appear obvious that the sun travels around the earth, for example, but this was nevertheless proved wrong. Similarly, it may appear obvious that apart from neural events there are also mental conditions, but that could be false.[23]
But even if one accepts the susceptibility to error of people's intuitions, the objection can be reformulated: if the existence of mental conditions seems perfectly obvious and is central to our conception of the world, then enormously strong arguments are needed to deny their existence. Furthermore, these arguments, to be consistent, must be formulated in a way that does not presuppose the existence of entities like "mental states", "logical arguments", and "ideas", lest they be self-contradictory.[50] Those who accept this objection say that the arguments for eliminativism are far too weak to establish such a radical claim and that there is thus no reason to accept eliminativism.[49]
Self-refutation[edit]
Some philosophers, such as Paul Boghossian, have attempted to show that eliminativism is in some sense self-refuting, since the theory presupposes the existence of mental phenomena. If eliminativism is true, then eliminativists must accept an intentional property like truth, supposing that in order to assert something one must believe it. Hence, for eliminativism to be asserted as a thesis, the eliminativist must believe that it is true; if so, there are beliefs, and eliminativism is false.[15][51]
Georges Rey and Michael Devitt reply to this objection by invoking deflationary semantic theories that avoid analyzing predicates like "x is true" as expressing a real property. They are instead construed as logical devices, so that asserting that a sentence is true is just a quoted way of asserting the sentence itself. To say "'God exists' is true" is just to say "God exists". This way, Rey and Devitt argue, insofar as dispositional replacements of "claims" and deflationary accounts of "true" are coherent, eliminativism is not self-refuting.[52]
Correspondence theory of truth[edit]
Several philosophers, such as the Churchlands and Alex Rosenberg,[41][53] have developed a theory of structural resemblance or physical isomorphism that could explain how neural states can instantiate truth within the correspondence theory of truth. Neuroscientists use the word "representation" to identify the neural circuits' encoding of inputs from the peripheral nervous system in, for example, the visual cortex. But they use the word without according it any commitment to intentional content. In fact, there is an explicit commitment to describing neural representations in terms of structures of neural axonal discharges that are physically isomorphic to the inputs that cause them. Suppose that this way of understanding representation in the brain is preserved in the long-term course of research providing an understanding of how the brain processes and stores information. Then there will be considerable evidence that the brain is a neural network whose physical structure is identical to the aspects of its environment it tracks and whose representations of these features consist in this physical isomorphism.[42]
Experiments in the 1980s with macaques isolated the structural resemblance between input vibrations the finger feels, measured in cycles per second, and representations of them in neural circuits, measured in action-potential spikes per second. This resemblance between two easily measured variables makes it unsurprising that they would be among the first such structural resemblances to be discovered. Macaques and humans have the same peripheral nervous system sensitivities and can make the same tactile discriminations. Subsequent research into neural processing has increasingly vindicated a structural resemblance or physical isomorphism approach to how information enters the brain and is stored and deployed.[41][54]
This isomorphism between brain and world is not a matter of some relationship between reality and a map of reality stored in the brain. Maps require interpretation if they are to be about what they map, and eliminativism and neuroscience share a commitment to explaining the appearance of aboutness by purely physical relationships between informational states in the brain and what they "represent". The brain-to-world relationship must be a matter of physical isomorphism—sameness of form, outline, structure—that does not require interpretation.[42]
This machinery can be applied to make "sense" of eliminativism in terms of the sentences eliminativists say or write. When we say that eliminativism is true, that the brain does not store information in the form of unique sentences, statements, expressing propositions or anything like them, there is a set of neural circuits that has no trouble coherently carrying this information. There is a possible translation manual that will guide us back from the vocalization or inscription eliminativists express to these circuits. These neural structures will differ from the neural circuits of those who explicitly reject eliminativism in ways that our translation manual will presumably shed some light on, giving us a neurological handle on disagreement and on the structural differences in neural circuitry, if any, between asserting p and asserting not-p when p expresses the eliminativist thesis.[41]