A summary of the AQA A-level philosophy, epistemology topic: Perception as a source of knowledge. Including definitions of terms, key theories, and the integral criticisms of them.
Perception as a Source of Knowledge Revision Document
Are the immediate objects of perception mind independent objects and their properties?
Our perception of such objects is sensitive to how the objects are, so differences in their
properties are detected by differences in our experience of them. (Highly intuitive- not certain)
Strengths:
● Common Sense: DR accurately describes how perception seems to us. We seem to experience objects in
an external world, not mental pictures of the world. This is a natural, instinctive belief.
● Simplicity: DR’s account of how perception works is simple – only perceivers and the external world exist
with no extra things (such as sense-data or God).
Criticisms of Direct Realism Responses
Argument from Illusion: Relational Properties:
● E.g. bent stick in water ● E.g. there is not actually anything
● Subjectively indistinguishable from bent, the stick has a property of
veridical perception looking bent in water
● In an illusion an object does not have ● In illusions we perceive relational
some property- we perceive it so it properties which are different to the
must instead be mental, e.g. sense intrinsic properties of objects
data ● We still directly perceive physical
objects and their properties
Argument from Perceptual Variation: Relational Properties:
● E.g. Russell’s table ● Properties of objects which depend on
● Different times/places/people can other things and the circumstances
have a different perceptual experience ● So the properties they ‘appear’ to
● Properties objects have vs what they have are still properties of the object-
appear to have are not identical so we both of which can be perceived
do not perceive objects directly directly
● Sense data are distinct from objects
so are a better explanation
Argument from Hallucination: The Disjunctive Theory of Perception:
● If we can perceive an object with ● Hallucinations and perception are two
some property that is a hallucination, different kinds of mental state- so you
it cannot be physical so must be can deny hallucinations are a type of
mental perception at all
● Hallucinations can be subjectively ● Seeming the same does not prove
distinguishable from veridical that they are the same thing
perception- we must see the same ● Hallucinations are imagining not
thing in both, e.g. sense data, directly perceiving- with no relation to the
because it is not physical objects actual world- there is no ‘cognitive
● E.g macbeth hallucinating a dagger contact’ like with perception
● So it is not correct to claim we
perceive sense data directly as
, opposed to physical objects
Argument from Time-Lag: How vs What We Perceive:
● Waves, e.g. sound and light, take time ● We do not perceive light waves
before reaching us to be sensed directly and physical objects indirectly
● E.g. light from the sun takes 8 minutes because we do not perceive light
to reach us- we perceive things as waves at all
they were 8 minutes before ● Light waves are just part of how we
● This is not perceiving reality so it must are able to to see physical objects- so
be perceiving something else although we perceive past events we
still perceive physical objects directly
What is different about sense-data and the external world it should represent?
External World Sense-Data
Material Mental (i.e. ideas)
Objective Subjective
Public Private
Permanent Temporary
Dubitable Indubitable
Are the immediate objects of perception mind-dependent objects (sense-data) that are caused by and
represent mind-independent objects?
Indirect Realism Arguments Criticisms Responses
Perceptual Variation & Illusions: DR responses to criticisms as ● Sense data is private so
● E.g. Russell’s table and criticisms of IR no two perceptions are
stick in water- indicates the exact same-
that what we perceive is (above) people's sense data is
not how the world is near identical for the
● Best hypothesis is that Scepticism About The Existence same place-time
we are perceiving the of Mind-Independent Objects: thought, so the best
same thing directly, e.g. ● Russell objects that we explanation is that they
sense data can know mind are perceiving the same
independent objects physical object (Russel
exist if we only have rejects this tho-
direct experience of assumes too much
sense data about other
● If IR is true we cannot people/sense data)
know that it is true… ● Russell’s cat proves
● Assuming that physical physical objects existing
objects exists- we is the best hypothesis
cannot know cause from (but even he admits you
effect cannot definitively solve
● It is a significant the problem of
weakness that mind scepticism)
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