Dualist theories — AQA A-Level Philosophy

Substance dualism holds that minds are a distinct kind of thing from bodies. On this view minds genuinely exist, but they are not the same as bodies, nor are they identical to any part of a body such as the brain or a region of it. The claim is about substances, that is, what fundamentally exists, not merely about properties. Learners should separate the existence claim (minds exist) from the non-identity claim (minds are not bodies or bodily parts), and see that both are needed. A useful test is to ask whether an option treats the mind as existing yet distinct from physical stuff, rather than reducing it to the brain or denying it altogether.

Descartes argues that the mind and body are distinct substances because they have different essential properties. His indivisibility argument runs: a body, being extended in space, can in principle be divided into parts, whereas the mind cannot be divided into parts, so the mind is not a body. Teach the learner to reconstruct the premises explicitly: bodies are divisible; minds are not divisible; things with different properties are not the same thing; therefore mind and body are distinct substances. A strong answer explains what 'divisible' means for each (spatial partition for body, loss of unified consciousness for mind), then evaluates: is the mind really indivisible, given divided attention, conflicting desires or brain damage? Does difference of property really prove difference of substance? The learner should assess, not merely describe, and reach a supported judgement.

This point is an objection to Descartes's indivisibility argument: although Descartes claims the mind is indivisible, the mental can plausibly be divided in some sense. Teach the learner to explain what 'divisible' could mean for mental life: attention can be split between tasks, desires and beliefs can conflict, emotions can be mixed, and consciousness can be disrupted or fragmented by injury or illness. The learner should show how these phenomena threaten the premise that the mind is a simple, indivisible unity, and therefore weaken the inference to a distinct mental substance. A strong answer weighs the objection against possible dualist replies, for example that such divisions are of contents or experiences rather than of the thinking substance itself, and reaches a judgement on whether the mental is genuinely divisible.

This point is a corrective to a common argumentative shortcut in substance dualism. A learner may reason: minds are indivisible, bodies are divisible, so minds are not bodies. The supplied claim warns that the second premise is too broad, because not everything we count as physical is divisible. Consider a point-particle in physics, or a fundamental particle treated as having no proper parts: it is physical yet not divisible into smaller physical pieces. Likewise an electron is physical but not split into halves. So 'divisible' cannot serve as a clean criterion separating all physical things from mental things. To use the point well, state the intended contrast precisely, restrict it to ordinary extended bodies, and explain why the counter-example weakens any argument that treats divisibility as the mark of the physical.

Descartes argues that because he can clearly and distinctly conceive of his mind existing without his body, mind and body must be really distinct substances. The version required here omits any appeal to God's power, so the inference runs from conceivability to genuine possibility to actual distinctness. Reconstruct it in steps: I have a clear and distinct idea of myself as a thinking thing with no bodily properties; whatever I can clearly and distinctly conceive as separate is capable of existing separately; therefore mind and body are distinct substances. Then assess it. A critic may say that conceivability does not guarantee real possibility, or that I may be conceiving an incomplete version of myself. A defender may appeal to the clarity and distinctness of the idea. Reach a reasoned judgement on whether the argument establishes substance dualism.

This claim is a premise used against substance dualism, not a description of how minds happen to work. The argument runs: if a mind could exist without a body, we should be able to conceive of a mind with no bodily or physical properties at all. Try it: strip away shape, location, mass, movement and every sensory quality, and ask what remains that you can positively imagine. The critic says nothing determinate remains, so the supposed separate mind is not genuinely conceivable, only the words are uttered. Conceivability is thus treated as a test of possibility: what cannot be coherently conceived is held not to be possible. Assess whether the test is applied fairly, since dualists may reply that we conceive minds through mental properties such as thinking rather than through imagery.

This principle separates two things: what we can coherently think or imagine, and what could actually exist. Conceivability is a feature of our concepts and imagination; metaphysical possibility concerns how reality could be. The gap matters for dualism because a dualist may argue that a mind without a body is conceivable and therefore possible. The critic replies that conceivability is a fallible guide: we may conceive of something coherently described that is nevertheless impossible, for instance because we lack full information about the nature of the thing. So the move from 'I can conceive it' to 'it is possible' needs justification. Assess whether any reliable link between conceivability and possibility can be established, and whether the dualist needs such a link.

This claim is a modal one: it says that establishing that something is metaphysically possible does not by itself establish anything about how the actual world is. Metaphysical possibility concerns what could obtain without contradiction across possible worlds; the actual world is one specific way things are. So a bare possibility claim leaves the actual facts open. For example, that zombies (physical duplicates without consciousness) are metaphysically conceivable and possible does not show that any actual being lacks consciousness. Learners should test the claim by asking what extra premise would be needed to move from 'possibly P' to 'actually P', and by distinguishing possibility from actuality and from conceivability. The correct option will treat possibility as failing to entail actuality, not as entailing impossibility or irrelevance.

Property dualism holds that there is only one kind of substance, the physical, but that at least some mental properties are neither reducible to physical properties nor supervenient upon them. 'Reducible' means analysable entirely in physical terms, so that the mental property is nothing over and above the physical. 'Supervenient' means that there can be no difference in mental properties without a difference in physical properties. Property dualism denies both for at least some mental properties: mental properties are genuine, irreducible features that are not fixed by the physical. Contrast substance dualism (two kinds of substance) and physicalism (mental properties reduce to or supervene on the physical). A correct option will keep the single-substance commitment while denying reducibility and supervenience for some mental properties.

Chalmers's zombie argument is a conceivability route to property dualism. A philosophical zombie is a being physically and functionally identical to a conscious human: same brain states, same behaviour, same dispositions to report experience, yet with no inner phenomenal feel. The argument runs: zombies are conceivable; whatever is conceivable is possible; so zombies are possible; if zombies are possible then consciousness is not identical with, or entailed by, the physical, so phenomenal properties are distinct from physical properties. This supports property dualism rather than substance dualism: one physical substance, two kinds of property. The key premise is that conceivability entails possibility, and the key reply is that it may not.

This is a critical response to Chalmers's zombie argument. The objector denies the first premise: a zombie world is not genuinely conceivable. One line is that if physical facts fully determine behaviour and reports, then a being claiming to feel pain while feeling nothing is incoherent, so the scenario cannot be consistently conceived. Another line is that our sense of conceiving a zombie is illusory, resting on incomplete physical knowledge. If zombies are not conceivable, the argument's first premise fails and the route to property dualism collapses. The reply is that we can clearly imagine such a being, so the dispute turns on what counts as genuine conceivability.

Jackson's knowledge argument supports property dualism by showing that physical information may be complete while phenomenal facts remain. Mary is confined and learns every physical fact about colour vision, including wavelengths, retinal and neural processes. On release she sees red for the first time and, Jackson claims, learns something new: what red looks like. If her complete physical knowledge did not include this, then experience involves non-physical properties. The argument targets property dualism, not substance dualism: it claims mental properties are irreducible to physical properties, not that a separate soul exists. Assess whether the 'new knowledge' is genuinely new fact or only a new way of representing old facts.

The ability knowledge response concedes Mary learns something on release but denies it is new propositional knowledge. Propositional knowledge is knowledge that something is the case, expressible in true statements. Ability knowledge is knowing how to do something, such as ride a bike or recognise a colour. On this view Mary already possessed every fact about red; seeing it gives her the ability to recognise, imagine and discriminate red experiences. So no new fact is added, and the physicalist can say her complete physical information was complete after all. Assess whether 'knowing what it is like' is purely a skill or also carries factual content, and whether the distinction is drawn too sharply.

This response to Mary's Room separates two kinds of knowledge. Propositional knowledge is knowledge that something is the case, expressible in true statements such as knowing that red light has a wavelength of about 700 nm. Acquaintance knowledge is knowledge of a thing gained by direct experiential contact, such as knowing what a colour looks like from seeing it. On this response, Mary's complete physical information already gives her every proposition she could state about colour vision, so when she leaves the black-and-white room she learns no new fact. What changes is her relation to the experience: she becomes acquainted with seeing red. The response therefore concedes that something is gained while denying that physicalism is refuted, because the gain is not propositional.

This response accepts that Mary learns something new when she first sees red, but denies that the new knowledge concerns a non-physical fact. The claim is that the fact she comes to know was already a physical fact contained in her complete physical information; what changes is the way she grasps it. Before leaving the room she knew the fact discursively, through descriptions and theory; afterwards she knows it experientially, through the experience itself. So the content is old, but the mode of presentation is new. This preserves physicalism because no extra non-physical fact is added. Assess it by asking whether knowing a fact in a new way really counts as new propositional knowledge, and whether the phenomenal character of experience can be captured by any mode of physical description.

Substance dualism holds that minds are non-physical substances distinct from bodies. This creates an epistemological problem: if mental states are private and inner, how can I know that anything else has a mind at all? I directly access only my own experiences; other bodies I observe behave and speak, but I never observe their consciousness. The problem of other minds presses the dualist because the very privacy that defines mental substance seems to block any inference to other minds. Learners should explain the asymmetry between first-person access and third-person observation, show why behaviour alone seems insufficient, and consider responses such as analogy, best-explanation reasoning and the behavioural criterion, weighing whether each preserves dualism or quietly abandons it.

The argument from analogy is a classic response to the problem of other minds. I notice that my own body behaves in certain ways when I have certain mental states: when I am in pain I wince and cry out. I observe other bodies behaving similarly, so by analogy I infer that they too have minds with similar experiences. Learners should reconstruct the inference carefully, identify its inductive structure, and evaluate it. Key criticisms include that it generalises from a single case, that it presupposes what it seeks to prove by relying on correlations established only in my own case, and that it cannot rule out philosophical zombies or behaviour without experience. Learners should also consider whether the analogy can be strengthened or whether it collapses into a behavioural criterion.

This claim is an inference-to-the-best-explanation argument for other minds, often used to defend dualism against the problem of other minds. The learner should reconstruct the reasoning: I observe that other bodies behave as mine does, and my own behaviour is caused by my mind, so positing minds in others explains their behaviour better than any alternative. Assessment rewards showing why the hypothesis is judged 'best' — it has explanatory power, predictive success and simplicity compared with behaviourism or the hypothesis that others are mere automata — and then weighing objections: the argument is an inference by analogy, it cannot be verified directly, and a physicalist explanation may be simpler. The learner must argue to a judgement, not merely describe the position.

Ryle's charge is that substance dualism treats the mind as a separate entity of a special kind, when mental language actually describes capacities and dispositions of the whole person. The learner should explain the category mistake: asking where the mind is, as if it were another place alongside the body, is like asking where the university is after being shown the colleges. Assessment rewards accurate explanation of Ryle's point, application to dualism's claim that mind and body are distinct substances, and evaluation — whether Ryle's behaviourist leanings can account for private experience, and whether dualists can reply that consciousness is not merely dispositional. The learner must argue to a judgement rather than merely report the criticism.

Elisabeth of Bohemia presses a conceptual difficulty for substance dualism: if mind and body are distinct kinds of substance, what could make their causal interaction intelligible? Her challenge is not merely that we lack a mechanism, but that the very description of an immaterial, unextended mind acting on an extended body seems to leave no coherent account of how one could move the other. Teach learners to reconstruct the argument: minds are thinking, unextended things; bodies are extended, mechanical things; causation between them is asserted but unexplained; therefore the dualist owes an account of the kind of causal relation involved.

The empirical interaction problem asks where and how mind and body could causally meet given what observation and science tell us about the physical world. If every physical event has a sufficient physical cause, an immaterial mind acting on the body appears to add nothing that could be detected, and its influence seems to be either redundant or in conflict with physical closure. Teach learners to distinguish this evidential, observation-based worry from the conceptual one: here the issue is fit with empirical findings, such as neural causation of behaviour and conservation of physical quantities, rather than the bare intelligibility of the relation.

Within dualist theories, the challenge of introspective self-knowledge is sharpest for epiphenomenalist property dualism. Epiphenomenalism holds that mental states are caused by physical brain states but are themselves causally inert: they are by-products that cause nothing. Introspection is supposed to give us knowledge of our own mental states. But if a mental state cannot cause anything, it cannot cause the introspective belief that I have it. So the belief 'I am now in pain' would be produced entirely by physical events, not by the pain itself. The objection is that epiphenomenalism makes introspective knowledge of experience mysterious or accidental: our beliefs about our minds are not reliably connected to the mental states they purport to report.

Phenomenology here means how mental life actually seems from the inside. Our experience does not present a stream of disconnected items: one thought leads to another, a memory triggers an emotion, a decision produces a bodily movement. Mental life seems to involve causal connections of two kinds. Psychological causation runs between mental events, as when anxiety about an exam leads to rehearsing worst cases. Psycho-physical causation runs between mind and body in both directions, as when a worry causes a racing heart, or a stubbed toe causes pain. The challenge for dualism is to make sense of these apparent connections if mind and body are distinct substances.

Natural selection is the evolutionary mechanism by which heritable variations that improve an organism's chances of surviving and reproducing become more common in later generations, while less advantageous variations tend to disappear. The challenge for dualism is that this process appears to explain human bodies, brains and behaviour entirely through physical causes, without needing a non-physical mind or soul. If mental capacities such as reasoning, emotion and consciousness arose gradually from physical evolution, a dualist must explain how and when an immaterial mind entered the picture, and why a purely physical account of the brain seems increasingly adequate.