Epiphenomenalism, however, has difficulties of its own. For one thing, it isn’t clear that physical-to-mental causation is any easier to understand than mental-to- physical causation. Second, and far more importantly, depriving the mental of causal powers simply goes against almost all of what we believe about mentality—that is, about us. To most of us it is just not believable to say that our desires and intentions have nothing to do with what we do, or that the same human civilization would have developed even if no humans had ever had a thought, an idea, or a hope. Mental causation is a simple matter for physical reduc- tionism, for it identifies mentality with physical processes, and this means that mental causation is simply a species of physical causation. But reductionism has not been a popu- lar option for some time. Non-reductive physicalism, which arguably is the current orthodoxy on the mind– body problem, encounters serious difficulties with the causal closure of the physical: if the physical domain is ‘causally closed’, as all serious physicalists believe, how can mental states, states that are irreducibly distinct from the physical, inject their causal influence into the physical domain? The problem of mental causation remains a central issue in the continuing debate over the nature of mind. 4. Intentionality. Wittgenstein asked: ‘What makes my image of him into an image of him?’ Many mental states, including thoughts, beliefs, and desires, are ‘intentional’ in Brentano’s sense—that is, they are ‘about’ or ‘directed upon’ an object. My thought that Boston is to the north of New York is about, and is directed upon or refers to, Boston and New York. As earlier noted, Brentano claimed that intentionality is the defining characteristic of mentality. Earlier debates on intentionality during the twentieth cen- tury (notably, R. M. Chisholm’s work) focused on the pro- ject of validating Brentano’s thesis by providing a precise definition of intentionality. Mentality, however, is not the only phenomenon with intentionality; our words and sen- tences, too, have meanings and can refer to, or be about, things. This gives rise to a profound question: Is the inten- tionality of mind more basic than, or prior to, the inten- tionality of language, or is it rather the reverse? Perhaps, neither is prior to the other, both being interdependent. Moreover, we seem to be able to have thoughts about things that do not exist, like Pegasus and the fountain of youth (surely Ponce de León had thoughts about the lat- ter). But how is it possible for our minds to direct them- selves upon things that do not exist? We are apt to think that our thoughts about Pegaus and our thoughts about Cerberus are about different things. But how can that be? Given that neither exists, why aren’t the thoughts about the same thing, namely nothing? Lately, however, the focus of discussion has shifted to the project of ‘naturalizing’ intentionality. It is useful to distinguish two problems here: the problem of ‘referential intentionality’ (or the problem of reference, for short) and that of ‘content intentionality’ (the problem of content). The first is the problem just reviewed, namely that of giving an account of the conditions under which a thought, or an expression, is about, or refers to, an object. The second is the problem of specifying the conditions under which a mental state has the specific ‘content’ or ‘meaning’ it has; that is, what it is about your belief that snow is white that makes it the case that its content is that snow is white, or that it represents the state of affairs of snow being white. The naturalization constraint in this context is usually taken to mean that any acceptable account of intentionality of either type must be formulated without the use of any unanalysed intentional or other overtly mentalistic concepts (for example, Frege’s notion of ‘grasping’ a thought or proposition and Chisholm’s notion of ‘conceiving’ a property). The causal approach has been the most popular in developing naturalistic accounts of intentionality. A causal theory of reference would attempt to explain ‘expression x refers to object y’ in terms of an appropriate causal relation holding between the uses of term x and object y; a causal theory of content would try to analyse ‘Person S has the belief that p’ in terms of a causal, or lawful, relationship between S’s belief that p and the state of affairs represented by p. Some philosophers have stressed the importance of the inferen- tial relations into which a thought enters in fixing its con- tent; others have focused on the constraints of rationality and coherence as central to the determination of a speaker-thinker’s mental contents. As this very brief sur- vey shows, many different approaches and perspectives are in play in this area, and the situation is still very fluid. One problem about content that has received much attention recently is content externalism. This is the view, first advanced by Hilary Putnam and Tyler Burge, that physical and social factors external to the subject play a crucial role in determining the contents of that subject’s beliefs and other intentional states. This means that what goes on ‘within’ you—your mind or your body—does not wholly determine the meanings of your thoughts or words (as it is put sometimes, meanings are not in your head). For example, you have the belief that water is wet, whereas your exact twin on ‘Twin Earth’, where water (that is, H 2 O) is replaced everywhere by a different but observationally indistinguishable substance, XYZ, has the belief that XYZ is wet, rather than the belief that water is wet. Or take a simpler example: you are looking at an apple, and your twin is also looking at an apple, which, as it happens, is qualitatively exactly similar to the one you are looking at. Your perceptual experience, let us say, is exactly similar to your twin’s. However, your thought that here is a red apple and your twin’s thought that here is a red apple have different contents—they are about different objects and their truth-conditions are different. This dif- ference in thought content seems to stem not from any internal physical or mental differences between you and your twin, but from differences in the external environ- ment. Just what the implications of content externalism are in regard to such questions as the truth of materialism, the causal powers of mental states, first-person epistemic 610 mind, problems of the philosophy of authority on one’s own mental states, and the nature of psychology as a science, are open questions. 5. *Consciousness. Thanks largely to the influence of behaviourism and positivism early in the twentieth cen- tury, consciousness was studiously avoided, or at least ignored, by both psychologists and philosophers as a topic for serious investigation for much of that century, a fact that may strike one as deeply paradoxical. For one might wonder how mentality could be discussed or studied without examining consciousness. The common-sense conception of mentality gives consciousness the pride of place. In 1904, Ivan Pavlov, in his Nobel Prize acceptance speech said: ‘In point of fact, only one thing in life is of actual interest for us—our psychic experience.’ But by the 1940s and 1950s, behaviourism was firmly established as the reigning orthodoxy in psychology and social science, and a well-known and influential psychology textbook defined psychology as ‘the science that studies the behav- ior of man and other animals’ (Ernest Hilgard, Introduction to Psychology, 3rd edn. (1953)). As it turned out, however, the reign of behaviourism was short-lived, and since the 1960s there has been a sea change in the philosophical and scientific perspectives on consciousness. With the loos- ening of behaviourist and hyper-empiricist constraints, consciousness has made a strong come-back, both in systematic psychology and in philosophy, and serious philosophical works on consciousness have been appearing again, in large numbers. The ill repute of consciousness was due in part to cer- tain questionable characteristics attributed to it by both friend and foe, such as absolute ineffability, immediate and infallible accessibility to the subject combined with a total inaccessibility to the third person, and its interper- sonal incomparability. It seemed to many that given these characteristics, consciousness could not be scientifically studied and explained, and, worse, that such essentially private experiences couldn’t even be talked about in pub- lic language. In so far as we are able to learn and use expressions like ‘pain’, ‘thought’, and ‘anger’ for interper- sonal communication, their meanings could not, it was argued, be fixed by some private episodes in an inner theatre accessible only to a single privileged subject. And surely we can, and do, use ‘pain’ and other mental expres- sions to communicate public meaning; how else could we explain a simple exchange like this: ‘Does this give you pain?’ (asks the dentist); ‘Yes, it does’ (the patient replies). Consciousness conceived as something essentially private and subjective thus seems to drop out of the picture, with no role to play in our public discourse, whether it is the language of science or the common language of every- day life. Much recent work in cognitive psychology, however, appears to assume all but explicitly that subjects of certain psychological experiments are having specific sorts of con- scious experience, such as mentally rotating an image. But the methodological assumptions that govern such refer- ences to consciousness are usually left vague and inex- plicit, and the issue of their justification is seldom openly addressed. There are two broad issues concerning con- sciousness in psychology: first, how useful consciousness is as an explanatory concept, a concept in terms of which psychological theories can be formulated to explain the data in their domain, and second, whether it is possible to explain consciousness itself scientifically. Views are divided on both questions. There still are those (elimin- ativists and epiphenomenalists) who either outright reject, or are dubious about, the explanatory utility of con- sciousness. Some argue, as the classic epiphenomenalist did, that any intelligent behaviour for whose explanation we are apt to invoke conscious states can be explained per- fectly well in terms of the underlying neural processes, and that this shows the dispensability of consciousness in psychology and cognitive science. Others have stressed the differences that consciousness supposedly makes to behaviour—e.g. performance levels of activities that require monitoring and control. There is also the meta- physical issue of whether or not it is ever necessary to invoke conscious states over and above their underlying neural substrates in the causal explanation of behaviour. Can consciousness be explained scientifically? There are those who accept consciousness as a natural phenom- enon arising out of physiological processes but despair of ever fully understanding it. Some have argued that the essential subjectivity of consciousness (i.e. the purported fact that all experiences involve a ‘point of view’ and are accessible only from the subject’s point of view) precludes scientific understanding, which, being entirely objective, is unable to accommodate subjectivity. More optimistic are those who pin their hopes on the concerted efforts of neuroscience and cognitive psychology for an eventual naturalistic understanding of consciousness. What isn’t clear in this debate is what exactly is required of a ‘scien- tific understanding’ of consciousness—that is, what spe- cific factual or theoretical information we need to obtain if we are to gain a scientific understanding of consciousness. Some who think that consciousness can be neurobio- logically explained appear to think that all that is needed for the success of their project is to identify a neural sub- strate for every type of conscious experience and for con- sciousness itself. Many will challenge this assumption, however, holding that these correlations are exactly what is in need of explanation. Suppose we discover that pains and itches are correlated respectively with neural states M andN. Why is it that pains, not itches, occur when Moccurs? Why is it that pains occur only when M occurs and not when N occurs? (Can neurobiology explain why pains, not itches, mediate between tissue damage and wincing, and why itches, not pains, come between mosquito bites and scratching?) Why does consciousness emerge at all when M or N occurs? Even the noted biologist-neuroscientist Francis Crick has observed: ‘we may be able to say that you perceive red if and only if certain neurons (and/or molecules) in your head behave in a certain way. This may, or may not, suggest why you experience the vivid sensation of color and why one sort of neural behavior mind, problems of the philosophy of 611 necessarily makes you see red while another makes you see blue, rather than vice versa’ (The Astonishing Hypothesis (New York, 1994), 10). Perhaps, these questions have no answers, and these correlations have to be taken as ‘brute facts’ of the world that resist further explanation—facts which Samuel Alexander, a leading emergentist, once claimed we must accept with ‘natural piety’. This of course would be to admit that consciousness could not be fully understood on a neurobiological or any other kind of physical basis. It is not an exaggeration to say that the ‘mystery of the mind’ is by and large the mystery of consciousness, and this mystery consists in our seeming inability to under- stand the phenomenon of consciousness as part of a world that is essentially physical, and, what is worse, not know- ing just what it is that we need to know if we are to achieve such an understanding. 6. *Persons. The nature of personhood has been a topic of perennial philosophical interest; it is one where philoso- phy of mind and moral philosophy come together, since a person is also an agent, someone who is able to deliberate, form intentions, and perform actions, and hence is evalu- able from the moral point of view. The question ‘What is a person?’ can be approached in two ways, synchronically and diachronically. Synchronically, the question concerns the properties and powers something must possess at a time to be a per- son at that time. It will generally be agreed that a person must have a rich mental life and be endowed with certain psychological capacities and functions. But what exactly is required? Evidently, a person must be capable of having intentional states such as beliefs, desires, and the rest if he, as an agent, is to be able to form intentions and decisions. Should a person also be conscious? Should she also be self- conscious in the sense of having a sense of self-identity and being aware of her distinctiveness as an individual person among others? Should a person be rational in some clear and determinate sense? There is also the following meta- physical question: Must a person be embodied or could there in principle be persons who are immaterial? A trad- itionalist, especially one who is religiously inclined, might answer that not only can a person be wholly immaterial but she must be possessed of an immaterial soul, an answer that will be rejected by most naturalistically inclined philosophers. At any rate, these are some of the questions that arise with respect to being a person at a time. The diachronic question, however, has received far more attention historically, and this continues to be true today. This is the so-called problem of ‘personal identity’: what makes a person existing at a given time (say, the retired general) the same person as one that existed at an ear- lier time (the little boy in the photograph). Persons, like anything else, change over time; both your mental and bodily characteristics change, sometimes rather strik- ingly, over a period of time, without your ceasing to be the same person. Changes could of course be so huge and drastic that it would be correct to say that you have ceased to exist, or that another person has come into being. But what general principles govern our judgements about such cases? There are two important approaches to this issue, both commanding the allegiance of many philoso- phers. One is the bodily continuity theory; it says that for you to be the same person as a person existing at another time, your body, or an appropriate part of your body, must be continuous, in some appropriate sense, with the body of that person—namely, that the continuity of embodiment is what underlies the identity of a person over time. The second is the psychological continuity the- ory, according to which the continuity of mental life— that is, the continuity of character, personality, and, in particular, memory—rather than bodily continuity, is what is constitutive of the sameness of a person. Many details need to be supplied: e.g. precisely what the sup- posed ‘continuity’ is supposed to consist in, and just when the required continuity must be considered broken. There is also the question whether psychological continuity can be considered independent, conceptually or nomo- logically, of bodily continuity. In any case, each of the two approaches appears vulnerable to persuasive counter- examples, and plausible arguments have been presented in recent years for the position that personal survival is a matter of degree, not an all-or-nothing affair, and that there are situations in which no clear-cut answer exists to the question ‘Has the same person survived?’ Although our understanding of these problems has been deepened in many ways in recent years, the concept of person- hood continues to test our philosophical ingenuity and imagination. j.k. *theory theory of mind; mind–body problem. D. Armstrong, A Materialist Theory of the Mind (London, 1968). N. Block, O. Flanagan, and G. Güzeldere (eds.), The Nature of Con- sciousness (Cambridge, Mass., 1997). T. Burge, ‘Individualism and the Mental’, Midwest Studies in Philosophy, v (1979). D. J. Chalmers, The Conscious Mind (New York, 1996). —— (ed.), Philosophy of Mind: Classical and Contemporary Readings (New York, 2002). R. M. Chisholm, The First Person (Minneapolis, 1981). P. M. Churchland, Matter and Consciousness, rev. edn. (Cam- bridge, Mass., 1988). P. S. Churchland, Neurophilosophy (Cambridge, Mass., 1986). D. Davidson, Essays on Actions and Events (Oxford, 1980). D. C. Dennett, Consciousness Explained (Boston, 1991). J. Fodor, Psychosemantics (Cambridge, Mass., 1989). T. Honderich, Mind and Brain (Oxford, 1988). J. Kim, Mind in a Physical World (Cambridge, Mass., 1998). J. Levine, Purple Haze (New York, 2000). Colin McGinn, The Problem of Consciousness (Oxford, 1991). D. Papineau, Thinking about Consciousness (Oxford, 2002). D. Parfit, Reasons and Persons (Oxford, 1984). H. Putnam, Mind, Language, and Reality (Cambridge, 1975). G. Ryle, The Concept of Mind (London, 1949). J. Searle, The Rediscovery of the Mind (Cambridge, 1992). S. Shoemaker, Identity, Cause, and Mind, 2nd edn. (Oxford, 2003). J. J. C. Smart, Philosophy and Scientific Realism (London, 1963). L. Wittgenstein, Philosophical Investigations (New York, 1953). 612 mind, problems of the philosophy of mind–body problem. The mind–body problem is the problem of giving an account of how minds are related to bodies, or how mental states and processes are related to bodily states and processes. That they are intimately related seems beyond doubt, and has not been seriously disputed. Evidently, our perceptual experiences depend on the way external physical stimuli impinge on our sen- sory surfaces, and, ultimately, on the processes going on in the brain; your desire for a drink of water somehow causes your body to move in the direction of the water-cooler; a bruised elbow causes you pain when it is touched, and the pain in turn causes you to groan and wince; and so on. But how do conscious experiences emerge out of the electro- chemical processes in a grey mass of neural fibres? How do our beliefs and desires manage to get the appropriate neurons to fire and thereby cause the right muscles to con- tract? Schopenhauer called the mind–body problem ‘the world knot’, a puzzle that is beyond our capacity to solve. The mind–body problem as it is now debated, like much else in contemporary philosophy of mind, has been inherited from Descartes. Descartes conceived of the mind as an entity in its own right, a ‘mental substance’, the essential nature of which is *‘thinking’, or *consciousness. In contrast, the defining nature of material bodies, or material substances, was claimed to be spatial extended- ness—that is, having a bulk in physical space. Thus, Descartes envisaged two disjoint domains of entities, one consisting of immaterial minds with their mental proper- ties (e.g. thinking, willing, feeling) and the other of mater- ial bodies with their physical properties (e.g. size, shape, mass, motion). For Descartes, not only did minds lack spa- tial extension; they were not in physical space at all. How- ever, the two domains are not to be entirely unconnected: a mind and a body can form a ‘union’, resulting in a human being. Although the nature of this ‘union’ relationship was never made completely clear, (Descartes claimed it to be a primitive notion that is intelligible in its own right), it evi- dently involved the idea that a mind and a body joined in such a union are involved in intimate and direct causal interaction with each other. Thus, Descartes’s mind–body doctrine combines sub- stance dualism, i.e. a dualism of mind and body, each con- ceived as an independent substance, with the idea that there is causal interaction between the two. Many of his contemporaries, like Leibniz and Malebranche, were sub- stance dualists, but they rejected the idea of mind–body causal interaction. They found it difficult to make sense of the idea that immaterial minds with neither extension nor mass, and not even in physical space, could somehow move material bodies with mass and inertia. Substance dualism, however, has largely dropped out of contempor- ary discussions, although it has by no means disappeared; few philosophers now find the idea of minds as immater- ial substances coherent or fruitful. There has been a near consensus, one that has held over almost a century, that the world is essentially physical, at least in the following sense: all that exists in the space-time world are bits of matter and complex structures aggregated out of bits of matter, and the space-time world is the whole world. If all matter were to be removed from this world, nothing would remain—no minds, no ‘entelechies’, no ‘vital forces’, and not even an empty space-time. According to this physical monism (or ‘ontological physicalism’), men- tal states and processes are to be understood as states and processes occurring in certain complex physical systems, such as advanced biological organisms, not as states of some ghostly immaterial beings. This means that the prin- cipal remaining project for contemporary discussions of the mind–body problem is that of explaining how the mental character of an organism or system is related to its physical nature. The heart of contemporary *physicalism is the primacy and priority of physical properties and the laws that gov- ern them. The following *‘supervenience thesis’ is one way of expressing this idea: once all the physical facts about your body are fixed, that fixes all the facts about your mental life. That is to say, what mental properties you instantiate is wholly determined by the features and characteristics of your bodily processes. In fact, the phys- ical facts of a world determine what mental facts will hold in that world; that is, if God were to make an exact physical duplicate of this world, it would necessarily be a mental duplicate as well. This thesis, often called ‘super- venience physicalism’, can be given different formulations of varying degrees of strength. But there is a sense in which emergentism, a form of non-physicalist dualism, is committed to mind–body supervenience; the emergentist will surely accept the claim that if two systems are phys- ically identical, they must be identical in respect of the non-physical (e.g. mental) properties that emerge in them. Many physicalists, therefore, want something stronger than mind–body supervenience. Granted that mental properties are supervenient on physical ones, they may yet be distinct from them, just as aesthetic properties of works of art, in spite of their supervenience on the works’ physical properties, seem to remain distinct from them. We know that mentality is subserved and determined by neural processes. But are mental properties ‘over and above’ their neural correlates? A negative response to this question constitutes the *identity theory of mind, or ‘type physicalism’, which identifies mental properties with their neural–physical correlates. So pain is identified with the excitation of C- fibres (assuming this to be its neural correlate); pain isn’t some shadowy epiphenomenon of a brain process—it is a brain process. And similarly for all other mental states and properties. This is a classic form of mind–body reduction- ism: mentality is not renounced or eliminated, but con- served as a neural process, and thereby becomes a legitimate subject of scientific inquiry. Among the argu- ments for this view of the mind–body relation are the following: the argument that this gives us the simplest overall picture of the world in which physical science can explain all the phenomena; the argument that the identification of a mental property (pain) with its neural correlate (C-fibre stimulation) gives the simplest and best mind–body problem 613 explanation of the observed correlation between them; and the argument that only by identifying mentality with a neural-physical process is it possible to explain how men- tality can have a causal influence in the physical world. Like *behaviourism, an earlier form of reductionism which attempted to identify mentality with facts about observable behaviour, type physicalism has failed to win enduring support. The most influential objection has been the variable (or multiple) realizability of mental kinds. Consider pain: there is no reason to expect that the same neural process underlies pain for all the different actual and possible pain-capable organisms (the neural substrate of pain is probably very different in humans and in octo- puses). Moreover, there seems no a priori reason to deny the capacity for pain to all inorganic, or non-biological, sys- tems. There seems then no single physical kind with which pain, as a mental kind, can be identified. Note, however, that supervenience physicalism as such is perfectly consist- ent with the variable realizability of mental properties. These considerations have led to the formulation of *functionalism, arguably the most influential position on the mind–body relation during the past four decades. Functionalism conceives of mental kinds as ‘functional kinds’, not physical kinds. Pain, for example, is to be understood in terms of its function as a causal intermedi- ary between sensory input (e.g. tissue damage), behaviour output (e.g. wincing, groaning, and escape behaviour), and other mental states (e.g. desire to be rid of it). An inter- nal state of an organism that serves this function, which can vary from species to species (and perhaps from indi- vidual to individual), is said to be a ‘realizer’ of pain. Most functionalists are physicalists in that they hold that only appropriate physical states could serve as realizers of men- tal states functionally conceived. But they differ from type-physicalists in holding that, on account of their vari- able realizability, mental states cannot be identified with physical–biological states. Functionalism construes psych- ology as an autonomous science of these functional properties and kinds, specified in terms of their causal roles and abstracted from their specific physical-biological realizations. This view of psychology has been influential; it can be considered the received view of the nature of cognitive science. The question whether or not function- alism is a non-reductive form of physicalism depends cru- cially on exactly what physical reduction requires, and it must be considered an open question. *Eliminativism urges that our commitment to mental- ity is nothing more than an outdated folklore, and that it is certain to be superseded by a more scientific understand- ing of our nature. Thus, the standard eliminativist argu- ment begins with the premiss that vernacular (‘folk’) psychology—in particular, the psychology of beliefs, desires, and other ‘propositional attitudes’—is infested with massive and irremediable systemic errors and gaps, and concludes that it will be made obsolete as the scien- tific—in particular, neuroscientific—understanding of our behaviour continues to advance. Beliefs and desires will ultimately meet the fate that befell phlogiston and magnetic effluvia, the forgotten posits of discarded the- ories. This eliminativist argument is sometimes advanced against intentional psychology countenancing cognitive states that are analogous to propositional attitudes of ver- nacular psychology. Recently, the Schopenhauerian *pessimism has been resurrected by some philosophers, who argue that the mind–body problem is insoluble, and that we will never be able to understand how consciousness, subjectivity, and intentionality can arise from material processes. In any case, one thing that is certain is that the mind–body problem is one of the deepest puzzles in philosophy, and that it will continue to test our philosophical intelligence and imagination. j.k. *eliminativism; emergence. D. Chalmers (ed.), Contemporary Philosophy of Mind (New York, 2002). P. M. Churchland, Matter and Consciousness, rev. edn. (Cam- bridge, Mass., 1988). J. Kim, Philosophy of Mind(Boulder, Colo., 1996). C. McGinn, The Problem of Consciousness (Oxford, 1991). T. Honderich, Mind and Brain (Oxford, 1988). D. Rosenthal (ed.), The Nature of Mind (Oxford, 1991). mind, syntax, and semantics. Mental phenomena such as beliefs, desires, hopes, fears, love, hate, perception, and intention are said to be *‘intentional’ in the sense that they are directed at or about or of objects and states of affairs in the world. These phenomena may be conscious or uncon- scious. All of these intentional mental phenomena have mental contents. Thus, for example, a belief is always a belief that such and such is the case, where the ‘that’ clause specifies the content of the belief. Some efforts have been made to analyse intentional mental states as computational states, but such efforts suf- fer from the following objection: The computational states could not be identical with the mental states because computational states are defined solely in terms of their syntax. That is, computation is a matter of the manipulation of symbols, for example, 0s and 1s, and these are defined purely in terms of their formal or syntactical features. But these could not be equivalent to mental states, because though mental states often have a syntax, they also have a semantics—a thought content or an experi- ential content. Thus, a person who thinks that the earth is round has not only the appropriate symbols going through his mind, but he attaches a *meaning, interpret- ation, or understanding to these symbols. It is this mean- ing, interpretation, or understanding which constitutes semantics. The argument against the view that intention- ality can be reduced to computation is simply that syntax is not equivalent to nor sufficient for semantics. j.r.s. *chinese room; functionalism. J. R. Searle, ‘Intrinsic Intentionality’, Behavioral and Brain Sciences (1980). —— ‘Minds, Brains, and Programs’, Behavioral and Brain Sciences (1980). —— Minds, Brains and Science (Cambridge, Mass., 1984). 614 mind–body problem minimax: see maximin. minimalism. The term describes philosophical positions that draw on few conceptual or ontological resources. One example would be Noam Chomsky’s use of the term to describe his recent attempt to rationally reconstruct our grasp of grammar; another would be the *redundancy theory of truth—the view that ‘p is true’ says no more than ‘p’. ‘Minimalism’ also describes a movement in the arts, which featured highly undifferentiated objects. This was philosophically problematic, but arguably rested on con- fusing the different roles played by some property of an object when considered as a work of art and when consid- ered as a mere real thing. d.m. Richard Wollheim, ‘The Work of Art as Object’, in On Art and the Mind (London, 1973). miracles. Usually defined as violations of a *law of nature by a supernatural being. Questions have been raised about how to articulate a notion of law of nature which is not exceptionless by definition, and how and whether such a definition applies to indeterministic laws of nature. Any argument that a miraculous event has occurred faces the tough challenge of showing both that the event in ques- tion did occur and that it was miraculous. A famous argu- ment from Hume’s chapter ‘Of Miracles’ shows how difficult a challenge this is to meet: to suppose that a mir- acle has occurred is to suppose that something has hap- pened contrary to the entire weight of inductive evidence supporting the law of nature. In Hume’s words ‘no testi- mony is sufficient to establish a miracle, unless the testi- mony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavours to establish’. n.l. David Hume, An Enquiry Concerning Human Understanding, sect. x. mixture of labour. According to John Locke, if an indi- vidual has laboured upon a previously unowned resource and left enough for others, then he has acquired private property rights in it irrespective of their consent. Thus, ‘Labour being the unquestionable Property of the Labourer, no Man but he can have right to what is once joyned to, at least where there is enough and as good left in common for others’ (ii. v. 27). Locke’s belief that God gave the world ‘to the use of the Industrious and Rational, (and Labour was to be his Title to it)’ (ii. v. 34) suggests a religious basis for his view. The foremost modern Lock- ean advocate of private property, Robert Nozick, notes that pouring a can of tomato juice into the sea can be regarded as losing rather than acquiring rights, and conse- quently stresses not the mixture of owned with unowned resources but the alleged non-detrimental effects of appropriation. a.d.w. *property. John Locke, Two Treatises of Government (Cambridge, 1988). mnemic causation. According to Russell (The Analysis of Mind (London, 1921)), a ‘kind of causation . . . in which the proximate cause consists not merely of a present event, but of this together with a past event’. The term origin- ated with psychologist Richard Semon, who held that ‘mnemic phenomena’ like remembering necessitate the postulation of intervening ‘engrams’ or ‘traces’, because ‘what is past cannot operate now’, a suggestion Russell, undeterred by the prospect of action at a distance, thought unduly ‘metaphysical’. j.heil *causality; memory. J. Heil, ‘Traces of Things Past’, Philosophy of Science (1978). Mochus. ‘Learned men’, said Robert Boyle, attribute ‘the devising of the atomical hypothesis . . . to one Moschus a Phenician.’ The learned men were relying chiefly on Sex- tus Empiricus and Strabo, who somewhat sceptically report Posidonius’ belief that ‘the ancient doctrine about atoms originated with Mochus, a Sidonian, born before the Trojan times’. Boyle’s contemporary Cudworth reports without dissent the bizarre suggestion that ‘this Moschus was no other than the Celebrated Moses of the Jews’. j.j.m. *atomism. I. G. Kidd, Posidonius: The Commentary (on L. Edelstein and I. G. Kidd (eds.), Posidonius: The Fragments), 2 vols. (Cambridge, 1988), ii.2. modality. The modal value of a statement is the way, or ‘mode’, in which it is true or false: e.g. certainly so (epi- stemic modality), currently so (temporal modality), neces- sarily so (logical modality). In logic, ‘modality’ usually means ‘logical modality’, that is, the logical *necessity or possibility of a statement’s truth or falsity. A modal *state- ment is one in which some (usually logical) modality is actually claimed: e.g. ‘It is not impossible that pigs should fly’, ‘Necessarily not everyone is below average intelli- gence’. On a simple view these features interconnect: e.g. the modal statement ‘Necessarily P’ is true just when ‘P’ has the modal value necessarily true. *Modal logic studies the logical relations of modal statements. s.w. *de re and de dicto. A. N. Prior, Formal Logic (Oxford, 1962), pt. iii, ch. 1. W. V. Quine, ‘Three Grades of Modal Involvement’, in The Ways of Paradox (New York, 1966). modality and metaphysics. There is an intimate relation between modality and metaphysics, because not only are the nature and ground of modal truth fundamental issues for metaphysics, but the primary task of metaphysics itself may be seen as that of charting the realm of possibilities. Empirical sciences such as physics may tell us, on the basis of observation and experiment, what kinds of objects, events, and processes actually do exist, but they cannot tell us what must exist, nor what could (but actually does not) exist. A priori sciences such as mathematics may disclose a limited range of necessary truths to us, such as the truths modality and metaphysics 615 of arithmetic, but appear to be limited in their scope of inquiry to certain domains of abstract entities, such as the numbers. Moreover, even the empirical sciences cannot tell us what actually does exist, in the absence of a prin- cipled account of what could and could not exist, of the sort that metaphysics alone is equipped to provide. For empirical evidence can only be evidence for the actual existence of something if the existence of that thing is at least possible. e.j.l. E. J. Lowe, The Possibility of Metaphysics (Oxford, 1998). modal logic. In classical *propositional logic all the oper- ators are truth-functional. That is to say, the truth or falsity of a complex formula depends only on the truth or falsity of its simpler propositional constituents. Modal logic is concerned to understand propositions about what must or about what might be the case, and it is not difficult to see how you might have two propositions alike in truth- value, both true say, where one is true and could not pos- sibly be false while the other is true but might easily have been false. For instance, it must be that 2 + 2 = 4, but while it is true that I am writing this entry it might easily not have been. Modal logic extends the well-formed for- mulae (wffs) of classical logic by the addition of a one- place sentential operator L (or ٗ) interpreted as meaning ‘it is necessary that’. Using this operator a one-place oper- ator M(or ◊) meaning ‘it is possible that’ may be defined as ~L~, where ~ is a (classical) negation operator, and a two- place operator — 3 may be defined as α — 3 β = df L(α⊃β), where ⊃ is classical material implication. In fact any one of L, M, or — 3 can be taken as primitive and the others defined in terms of it. In the early days of modal logic disputes centred round the question whether a given principle of modal logic was correct or not. Typically these disputes involved formulae in which one modal operator occurs within the scope of another—formulae like Lp ⊃ LLp. Is a necessary propos- ition necessarily necessary? A number of different modal systems were produced which reflected different views about which principles were correct. Until the early 1960s, however, modal logics were discussed almost exclusively as axiomatic systems without access to a notion of validity of the kind used, for example in the truth-table method, for determining the validity of wffs of the classical propos- itional calculus. The semantical breakthrough came by using the idea that a necessary proposition is one true in all *possible worlds. But whether another world counts as possible may be held to be relative to the world of origin. So an interpretation or model for a modal system would consist of a set W of possible worlds and a relation R of accessibility between them. For any wff α and world w, Lα will be true at if and only if α itself is true at every w’ such that wRw′. It can then happen that whether a principle of modal logic holds or not can depend on properties of the accessibility relation. Suppose that R is required to be tran- sitive, i.e. suppose that for any worlds w 1 , w 2 , and w 3 , if w 1 ,Rw 2 and w 2 Rw 3 then w 1 Rw 3 . If so then Lp ⊃ LLp will be valid, but if non-transitive models are permitted it need not be. If R is reflexive, i.e. if wRw for every world w, then Lp ⊃ p is valid. So different systems of modal logic can rep- resent different ways of restricting necessity. First-order predicate logic can also be extended by the addition of modal operators. The most interesting conse- quences of such extensions are those which affect ‘mixed’ principles, principles which relate quantifiers and modal operators and which cannot be stated at the level of modal propositional logic or non-modal predicate logic. Thus ∃xL α⊃L∃xα is valid but L∃xα⊃∃xLα is not. (Even if a game must have a winner there need be no one who must win.) In some cases the principles of the extended system will depend on the propositional logic on which it is based. An example is the formula ∀xL α⊃ L∀xα, which is prov- able in some modal systems but not in others. If both directions are assumed, so that we have ∀xL α≡L∀xα, then this formula expresses the principle that the domain of individuals is held constant over all possible worlds. When identity is added even more questions arise. The usual axioms for identity easily allow the derivation of (x = y) ⊃ L(x = y), but should we really say that all identities are necessary? Questions like this bring us to the boundary between modal logic and metaphysics and remind us of the rich potential that the theory of possible worlds has for illuminating such issues. The possible-worlds semantics can be generalized to deal with any operators whose meanings are operations on propositions as sets of pos- sible worlds and form a congenial tool for those who think that the meaning of a sentence is its truth-conditions, and that these should be taken literally as a set of possible worlds—the worlds in which the sentence is true. m.j.c. B. F. Chellas, Modal Logic: An Introduction (Cambridge, 1980). G. E. Hughes and M. J. Cresswell, An Introduction to Modal Logic (London, 1968; repr. corr. 1972). —— —— A Companion to Modal Logic (London, 1984). modal realism. Rightly or wrongly, modal realism has come to be identified with David Lewis’s seemingly extravagant view of the ontological status of *possible worlds, according to which each possible world is an aggregate of spatio-temporally and causally interrelated concrete objects, and all such worlds equally exist. On this view, the world that we inhabit—what we call the actual world—is in no way ontologically privileged, since every world is ‘actual’ to its own inhabitants. Modal realism, thus understood, involves a commitment to *counterpart theory, which denies that objects existing in different pos- sible worlds can ever be identical, allowing each object only to have ‘counterparts’ in other worlds. For Lewis, modal realism is to be contrasted with ersatzism, which takes possible worlds to be linguistic or abstract entities, such as maximal consistent sets of sentences or propos- itions. Arguably, however, the term ‘modal realism’ might better have been employed to denote the more sober view that modal truths simply have an objective and mind-independent status. e.j.l. D. Lewis, On the Plurality of Worlds(Oxford, 1986). 616 modality and metaphysics mode. ‘Mode’ is a term of traditional metaphysics used correlatively with *‘substance’ and ‘attribute’. An example would be the square shape of a particular piece of wood. Here the wood is the substance possessing the mode, and spatial extension is the attribute of which the mode is an instance. Another example would be a particular thought or experience enjoyed by someone. Here the person (or *self ) qualifies as the ‘substance’ possessing the mode, and consciousness is the attribute. A crucial logical feature of modes is that they depend for their identity upon the identity of the particular sub- stances which possess them. Thus, that a thought is the particular thought it is is partly determined by whose thought it is. For two different people cannot share numerically the same thought. The modern term closest in sense to ‘mode’ is ‘particular quality’ or *‘individual property’. e.j.l. E. J. Lowe, ‘Real Selves: Persons as a Substantial Kind’, in D. Cockburn (ed.), Human Beings (Cambridge, 1991). model theory. When a set of sentences contain symbols that need interpreting, an interpretation that makes the sentences true is called a ‘model’ of the set. In 1954 Alfred Tarski introduced the name ‘model theory’ for the study of this notion when the sentences are mathematical axioms and the interpretations are mathematical struc- tures in which the axioms are true or false. A structure M is said to be a model of a set S of formal sentences if the sen- tences in S, when their formal symbols are interpreted as being about M, are all true. An early result of model theory says that if T is a set of sentences in a first-order language and every finite subset of T has a model, then T itself has a model. Within mathematics, model theory became a vehicle for studying definability, with applications in alge- bra and geometry; an offshoot was non-standard analysis, which justified the use of infinitesimals in calculus. Within philosophy and linguistics, an approach is called model- theoretic if it involves set-theoretical criteria for the truth of sentences, as for example in *Montague semantics. w.a.h. K. Doets, Basic Model Theory (Stanford, Calif., 1996). models. These are used extensively by scientists, coming in different forms and guises. All types involve some kind of analogy between the model and either reality or some other scientific claim. Most familiar are physical models, usually small- or large-scale material constructions—a famous example being the metal macro-model of the dou- ble helix, built by Watson and Crick. As or even more important are theoretical models, where scientists try to map limited aspects of reality, introducing simplifying assumptions, which are adjusted or removed in the light of the models’ predictive successes. There is a school of thought which argues that scientific *theories are best understood semantically, in the sense of being families of theoretical models—interpreted according to specific empirical circumstances—rather than as general systems attempting to explain selected chunks of reality at one fell swoop. Even if one protests that such families could never capture completely what one aims for in a theory, it is hard to deny that sets of interrelated models are what face sci- entists most of their working lives. m.r. P. Achinstein, Concepts of Science (Baltimore, 1968). R. Giere, Explaining Science (Chicago, 1988). modernism. On the longest view, modernism in philoso- phy starts out with Descartes’s quest for a knowledge self- evident to reason and secured from all the demons of sceptical doubt. It is also invoked—with a firmer sense of historical perspective—to signify those currents of thought that emerged from Kant’s critical ‘revolution’ in the spheres of epistemology, ethics, and aesthetic judge- ment. Thus ‘modernity’ and ‘enlightenment’ tend to be used interchangeably, whether by thinkers (like Haber- mas) who seek to sustain that project, or by those—the post-modernist company—who consider it a closed chap- ter in the history of ideas. c.n. *post-modernism. Jürgen Habermas, The Philosophical Discourse of Modernity, tr. Frederick Lawrence (Cambridge, 1987). modus ponens. The ‘affirming mode’. In *propositional calculus, any inference of the form ‘If p then q, and p; there- fore q’ is an instance of modus ponens. In the *traditional logic of terms, inferences like ‘If A is B, it is C; A is B; there- fore A is C’ were said to be in the modus ponens. Not really *syllogisms at all, such inferences were often called ‘hypo- thetical syllogisms’. c.w. *affirming the antecedent. J. N. Keynes, Formal Logic, 4th edn. (London, 1906), 352. modus tollens. The ‘denying mode’. In *propositional calculus, any inference of the form ‘If p then q, and not q; therefore not p’ is an instance of modus tollens. In the *trad- itional logic of terms, inferences like ‘If A is B, it is C; A is not C; therefore A is not B’ were said to be in the modus tollens. Like modus ponens inferences, not really *syllogisms at all. These inferences too were often called ‘hypothetical syllogisms’. c.w. *denying the consequent. J. N. Keynes, Formal Logic, 4th edn. (London, 1906), 352. Molina, Luis de (1535–1600). Jesuit theologian and philosopher, born in Cuenca, Spain. He studied and taught at various leading Iberian universities. Molina is best known for his doctrine of middle knowledge (scientia media), expounded in Concordia liberi arbitrii cum gratiae donis (1588). This doctrine’s aim was to preserve human *free will while maintaining the Christian doctrine of the efficacy of divine grace. For Molina, although God has foreknowledge of what human beings will choose to do, neither that knowledge nor God’s grace determine human will. Middle knowledge, God’s knowledge of what persons would do under any set of circumstances, enables Molina, Luis de 617 God to arrange for certain human acts to occur by pre- arranging the circumstances surrounding a choice with- out determining the human will. God’s grace is concurrent with the act of the will and does not predeter- mine it, rendering the Thomistic distinction between suf- ficient and efficacious grace superfluous. j.g. e.m. Alfred J. Freddoso, On Divine Foreknowledge: Part IV of the Concor- dia. With an Introduction and Notes (Ithaca, NY, 1988). Molla¯S . adra¯ (?–1641). Persian philosopher S . adr al-Dı¯n Shı¯ra¯zı¯ is widely considered to be one of the most original thinkers in post-classical Islamic philosophy. His most widely quoted philosophical problem (one of twelve con- sidered original contributions) is ‘substantial *motion’, the unifying principle underlying all of philosophy and capable of describing existence, time, motion, and change pertaining to all physical, psychological, and non-corporeal things. This problem, encountered in every domain from semantics to eschatology, consists of: essential motion initially observed in external reality, never ceas- ing, and covering all physical and ontological distinctions, resulting in the continual ‘evolution’ of higher beings, transformation of material existence, intensely moving from one level to another into the unchanging mundus imaginalis beyond ordinary time and space where individ- ual ‘evolved’ essences with ‘formal’, or ‘imaginalis’ bodies will then permanently exist. h.z. Fazlur Rahman, The Philosophy of Mulla¯S . adra¯(Albany, NY, 1975). Molyneux problem. A problem about correlating visual and tactual *perception, one of several that William Molyneux of Dublin posed in letters to John Locke. (Molyneux was also interested in the visual perception of distance.) Suppose that a blind person who can distinguish spheres from cubes by touch suddenly becomes able to see. Will this person be able to distinguish these shapes visually before correlating sight and touch? Locke (Essay Concerning Human Understanding, ii. ix. 8) and Berkeley (Essay Towards a New Theory of Vision, sects. 121–46) answer negatively. Berkeley went on to deny that sight and touch ever perceive the same property, strictly speak- ing. Leibniz (New Essays Concerning Human Understanding, sections that correspond to Locke) answers positively on the basis of structural properties in common to tactual and visible shapes. Careful observations of patients who acquired vision by surgery, such as cataract removal, have not resolved the Molyneux problem. d.h.s. Gareth Evans, ‘Molyneux’s Question’, in Collected Papers, (Oxford, 1985). Michael J. Morgan, Molyneux’s Question (Cambridge, 1977). monadology. A philosophical system usually associated with the mature metaphysics of Leibniz, as outlined in the Monadology (1714). The fundamental thesis of Leibniz’s monadology is that the basic individual *substances that make up the universe are soul-like entities, the monads, which are non-extended, hence immaterial, entities. The properties of the monads may all be reduced to perceptions and appetites. Whatever other entities we may wish to recog- nize must be reduced to this base. Thus Leibniz treated material objects as appearances of collections of monads. r.c.sle. monism, anomalous: see anomalous monism. monism, neutral: see neutral monism. monism and pluralism. These are doctrines concerning how many *substances exist, and may relate either to kinds of substances or to their individual instances. Monism regarding the kinds of substance holds that only one such kind exists, whereas pluralism admits a multi- plicity of kinds. Monism regarding the instances of a given substantial kind holds that only one such individual does or can exist, pluralism that many do or may. Thus a materi- alist who is also an atomist is a monist as regards the kinds of substance that exist but a pluralist with regard to how many individual substances of that kind there are. By contrast, Descartes was a pluralist as regards the kinds of substance that exist and also a pluralist regarding the num- ber of individual mental substances—but, rejecting *atomism, he was a monist regarding the number of indi- vidual material substances. e.j.l. D. W. Hamlyn, Metaphysics (Cambridge, 1984). Montague, Richard (1930–71). American philosophical logician. During the 1960s he developed a mathematical formalism to define what it is for a sentence of a precisely defined fragment of English to be true at a time and place in a possible world. Under the name of ‘Montague seman- tics’ his proposals soon became accepted among linguists as a paradigm for formalizing the semantics of natural lan- guages. Two characteristic points were his treatment of the meaning of a sentence as a homomorphic copy of its syntax (following Tarski’s truth definitions for formalized languages) and his proposal to treat proper names like ‘John’ as a special case of quantifier phrases such as ‘every man’ or ‘a fish’. Montague’s other contributions include work on the metamathematics of set theory, a study with David Kaplan of the paradox of the unexpected examin- ation, a logical analysis of determinism, and unsurpassed standards of rigour and accuracy in philosophical logic. w.a.h. R. Montague, Formal Philosophy, ed. R. H. Thomason (New Haven, Conn., 1974). Montaigne, Michel Eyquem de (1533–92). A fluent essay- ist who mistrusted the pretensions of systematic philoso- phy, Montaigne’s writings are richer in allusion and anecdote than in formal argumentation, but none the less sparkle with philosophical insights. His Apology for Ray- mond Sebond (1580) is an entertaining and discursive essay, steeped in the classical learning which typifies the human- ist movement of which he was a notable exemplar. The 618 Molina, Luis de book examines some of the sceptical theses of Sextus Empiricus (whose writings had recently been translated into Latin), and maintains the need for faith and divine revelation to overcome the inherent limitations of human reason. It also suggests that the supposed superiority of human reason over the natural instincts of animals is largely illusory. Montaigne’s writings set the scene for the attempts of rationalists such as Descartes to establish a new a system of knowledge whose foundations would be independent of the deliverance of the senses. j.cot. *rationalism. R. A. Sayce, The Essays of Montaigne: A Critical Exploration (Lon- don, 1972). Monte Carlo fallacy: see gambler’s fallacy. Montesquieu, Charles-Louis de Secondat, Baron de (1689–1755). French philosopher and jurist, who con- tributed to political sociology and to philosophy of his- tory. Persian Letters (1711, tr. New York, 1973) initiated the fashion of criticizing European culture by comparing it with the Orient. Considerations on the Causes of the Greatness of the Romans and their Decline (1734, tr. New York, 1965) and The Spirit of the Laws (1748, tr. Cambridge, 1989) dis- tinguish three forms of government, each with its special structure and each animated by its own ‘principle’. Republics are animated by virtue (patriotism and egalitar- ian fraternity rather than moral virtue), monarchies by honour, and despotisms by fear. Forms of government depend in part on physical, especially climatic, factors. But wise legislators can counteract physical disadvantages by intellectual and moral forces, especially once they know the laws governing the social world. Montesquieu’s advo- cacy of a division of powers (legislative, executive, and judicial), which he saw in the English constitution, greatly influenced the American founding fathers. m.j.i. M. Richter (ed.), The Political Theory of Montesquieu (Cambridge, 1977). Monty Hall problem. Game show host Monty Hall con- ceals a prize behind one of three curtains, A, B, or C. Asked to guess where the prize is, you choose A. Before disclos- ing the prize’s location, Monty opens B, revealing that it is not there, and offers you the option of sticking with A or switching to C. You reason as follows: once Monty opens curtain B, the *probability that the prize is behind A or C is the same: ½; so switching affords no advantage. But is this right? Assuming that Monty opens a curtain only if the prize is not behind it, the relevant probability is the *condi- tional probability that the prize is behind A given that Monty has revealed that it is not behind B. Bayes’s the- orem shows that this probability is ⅓, so the probability that the prize is behind C is ⅔. You should switch! For those not steeped in probability theory, there is a simple way to see the point. Once Monty opens a curtain, you will win by switching just in case your original choice was wrong. Assuming your original choice is wrong two-thirds of the time, you will win by switching two- thirds of the time, so you should switch. j.heil Martin Gardner, ‘Probability Paradoxes’, Skeptical Inquirer (1992). mood. States of mind of an emotional cast which are tem- porary, yet which colour a person’s responses and reac- tions quite generally, qualify as moods, as when someone is said to be in a sombre, sullen, or sunny mood. The focus is on a pattern of behaviour manifesting a current state of mind, and not, as with motives, on the intended conse- quences of the behaviour. ‘Mood’ also enjoys a use with respect to language. Commonly misconstrued in this connection, mood is properly a feature of verbal phrases—indicative, impera- tive, subjunctive, optative. As embodying the different speech-acts of asserting and asking a question, utterances of, say, ‘He is out’ and ‘Is he out?’ are said to differ in force. However, they agree in mood, the verb in either receiving the same description, ‘third-person singular present indicative’. b.b.r. *emotion and feeling. J. Lyons, Semantics, ii (Cambridge, 1977). G. Ryle, The Concept of Mind (London, 1948). moods of the syllogism: see syllogism. Moore, George Edward (1873–1958). Moore was a philosopher of immense, even revolutionary, influence by reason—most unusually—of the extreme simplicity and directness, even seeming naïvety, of his approach to philosophy. He was moved in his early days, as he recorded in 1942, not by any perplexities about ‘the world or the sciences’, but by the baffling things said about the world and the sciences by other philosophers. In the trad- ition prevailing at that time he found it usually taken for granted that ordinary language was probably defective, that commonly held beliefs were probably false or at any rate inadequate, and that the task of philosophy was to work its way towards deeper, perhaps odd-looking truths set out in purer, probably novel and unfamiliar terms. Moore was sincerely amazed by this. Why was it thought necessary? He insisted (‘A Defence of Common Sense’ (1925)) that there is actually a vast body of shared convic- tions about ‘the world’, expressible in quite ordinary propositions whose meanings are perfectly clear, and which are known for certain to be true—even by those philosophers who appear to deny them. Take, say, ‘There exist conscious beings other than oneself’—everyone knows what that means; or take, say, ‘There exist material objects, such as shoes and inkstands’—everyone knows that that is certainly true. But if so, Moore concluded, philosophers must have been radically confused as to the nature, or perhaps the purpose, of their own activities. They cannot really have been confronting problems about meaning, since typically there were, he held, simply no such problems; nor can they really have been denying, or even doubting, that certain propositions were true, Moore, G. E. 619 . than, or prior to, the inten- tionality of language, or is it rather the reverse? Perhaps, neither is prior to the other, both being interdependent. Moreover, we seem to be able to have thoughts. manage to get the appropriate neurons to fire and thereby cause the right muscles to con- tract? Schopenhauer called the mind–body problem the world knot’, a puzzle that is beyond our capacity to. of modes is that they depend for their identity upon the identity of the particular sub- stances which possess them. Thus, that a thought is the particular thought it is is partly determined