Perception Theories Flashcards Flashcards

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Direct Realism

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The view that the immediate objects of perception are mind-independent objects and their properties. It is a common-sense theory claiming we perceive the external world directly, e.g., seeing a tree is directly perceiving that tree. Direct realism faces challenges from variation, illusion, hallucination, and time-lag arguments.

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Indirect Realism

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The view that the immediate objects of perception are mind-dependent sense data that are caused by and represent mind-independent objects. We do not perceive the external world directly but infer it from our private perceptual contents. Indirect realism aims to explain disagreements between perception and reality by positing a representational intermediary.

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Idealism

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The view that the immediate objects of perception are mind-dependent ideas and that no mind-independent external world exists. Idealism holds that to be is to be perceived (esse est percipi), so reality consists of ideas rather than physical objects. Berkeley famously argues that what we call physical objects are sustained as ideas, ultimately by God’s perception.

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Sense Data

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The private, mental contents of perceptual experience posited by indirect realists as the immediate objects of perception. Sense data are caused by mind-independent objects and represent those objects, but they themselves are non-physical and only directly accessible to the subject. Their privateness gives rise to sceptical worries about the external world.

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Primary Qualities

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For Locke, primary qualities are properties inherent in an object itself, such as size, shape, motion, and number. They are treated as objective features that exist in the object independently of observers. Indirect realists use this distinction to argue that some aspects of objects are mind-independent.

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Secondary Qualities

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For Locke, secondary qualities are the powers of objects to produce sensations in observers, like colour, taste, smell, and sound. These qualities are subjective and depend on the perceiver’s sensory apparatus rather than existing wholly in the object. They help explain why perceptions can differ between observers.

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Russell Variation

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Bertrand Russell’s argument from perceptual variation notes that different observers often perceive different properties (e.g., colour patches or shape) of the same object. This variation challenges direct realism because the object cannot simultaneously possess mutually exclusive properties as perceived. Russell uses this to motivate representational accounts or relational refinements.

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Relational Properties

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A direct realist response that treats many perceived properties as relational, varying with the relation between object and perceiver. For example, an object can have the mind-independent property of appearing kite-shaped relative to one observer and square relative to another. This preserves direct perception while explaining perceptual variation as changes in relational properties rather than errors in perception.

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Argument from Illusion

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The argument that perceptual illusions (e.g., a straight pencil appearing crooked in water) show a discrepancy between perception and reality, challenging the claim that perception presents the world as it truly is. This undermines naive direct realism because perception can misrepresent the external object. Direct realists may reply using relational properties, but illusions remain a serious puzzle.

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Argument from Hallucination

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A stronger challenge to direct realism noting that hallucinations involve perceptual experiences of things that do not exist. If perception is always of mind-independent objects, hallucinations are inexplicable; hence hallucinations suggest that perceptual experience can occur without corresponding external objects. Some direct realists deny hallucinations are genuine perceptions, treating them as imaginations instead.

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Time Lag Argument

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The claim that because perceptual information (e.g., light) takes time to travel, we always perceive objects as they were in the past rather than as they are now. For example, seeing the sun as it was eight minutes ago shows a temporal gap between object and perception. Direct realists reply that the temporally delayed object is still a mind-independent object, so perception remains direct despite latency.

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Veil of Perception

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A sceptical problem for indirect realism asserting that if we only ever perceive sense data, we cannot know whether those data accurately represent a mind-independent world behind them. This ‘veil’ blocks direct access to external reality and can lead to radical scepticism about the existence or nature of the external world. Critics say this makes indirect realism epistemically costly.

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Russell Best Hypothesis

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Bertrand Russell’s indirect-realist reply to scepticism: the existence of a mind-independent external world is the best hypothesis to explain the coherence, continuity, and causal connections of our sense data. Russell concedes we cannot conclusively prove the external world but argues that positing it offers the simplest and most explanatory account of our experiences. This is an abductive or inference-to-best-explanation response.

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Locke: Involuntary Perception

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Locke’s response to scepticism emphasizes that perceptual experiences are involuntary and differ from imagination or memory, suggesting an external cause. Because we cannot control these perceptions at will, Locke infers that something external must be producing them. However, this does not by itself guarantee that sense data accurately represent the external world.

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Locke: Coherence of Senses

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Locke also argues that the agreement between different senses (e.g., seeing and feeling heat from a fire) supports the existence of mind-independent objects causing those experiences. Cross-sensory coherence makes it less plausible that perceptions are mere fictions. Critics reply that coherence between senses could still arise from correlated illusions or internal processes.

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Berkeley Master Argument

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Berkeley’s master argument contends that one cannot conceive of an object existing unperceived, because any supposed conception of such an object is itself a mental idea. From this he concludes mind-independent objects are inconceivable and therefore impossible. Critics point out that conceivability of an idea does not entail metaphysical impossibility of external objects.

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Berkeley on Primary Qualities

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Berkeley attacks Locke by arguing that primary qualities (size, shape, motion) are as mind-dependent as secondary qualities, since perceptions of them vary with observer and conditions. He claims we only ever perceive qualities, never some extra inert substance underlying them. This undermines the primary/secondary distinction and supports his idealism.

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God as Perceiver

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Berkeley invokes God as the cause and sustainer of ideas: God perceives all things continuously, ensuring that objects persist when finite minds are not perceiving them. God explains shared perceptions because finite minds perceive the same ideas sustained in God’s mind. This theological move is intended to solve problems of object persistence and intersubjective agreement for idealism.

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Solipsism

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The view that only one’s own mind exists and everything else is a product of that mind. Idealism can seem to lead to solipsism because if objects are mind-dependent, one might doubt the existence of other minds or objects when not perceived. Berkeley avoids solipsism by positing God and other minds as real causes of the ideas we perceive.