Direct realism
The argument
from perceptual
variation
The argument
from time-lag
The argument
from illusion
The argument
from hallucination
We perceive physical object directly and they exist
in independently of our minds
Different percipients perceive the same object
differently. Perceptions change over time, without
the object changing (eg as the lighting changes)
It takes time for any perceptual information to reach
our sense organs. What we see around us now
comes from objects at different times.
We frequently aspects of objects which do not
reflect their physical properties : eg a pencil looks
bent when seen partly through water
Occasionally we perceive things which are entirely
mental –like waking dreams–which are subjectively
indistinguishable from veridical perception.
Indirect realism
We perceive sense-data which are caused by and
represent objective reality
the distinction
between Primary
and secondary
qualitites
Idealism
Primary = utterly inseparable from the object =
extension, shape, motion, number & solidity.
Secondary = powers to produce certain sensations in
us = colours, tastes, sounds and so on
The immediate objects of perception are minddependent : Reality is essentially mental. Esse es
percipi
The inseparability
of primary &
secondary qual’s
The lack of a
material
substratum
The difference
between sensedata an physical
objects
The master
argument
You cannot conceive of a primary quality without
reference to a secondary quality. Primary qualities
are not independent of perception
If physical objects exist independently then there
must be substance which they are made of/holds
them together.
The essential qualities that apply to all sense data
are very different from the those that apply to
physical objects. So much so that it is unclear how
sense data can represent physical matter
“if you can conceive it to be possible for any mixture
or combination of qualities, or any sensible
whatever, to exist outside the mind, then I will grant
it to be so”
If reality is essentially mental, then objects which are
unperceived do not exist.
Solipsism (possibly) follows.
If reality is essentially mental then what is the
difference between hallucinations and veridical perc.
The problem of
unperceived
objects
The problem of
hallucinations
In favour : everyday language implies that this is the
relation that exists between what we perceive &reality
In favour : an argument against direct realism. How can
two people claim to see the same object directly, if they
perceive different things?
In favour : an argument against direct realism. When
looking at a bird flying in from of the sun, one aspect of the
perception is 8 minutes older than the other.
In favour : an argument against direct realism. If the pencil
is straight and we see it bent then we must be seeing
something other than the physical objects directly
In favour : an argument against direct realism in
hallucinations we do not perceive physical reality, we
experience sense-data. What we perceive in veridical
perception must be the same.
In favour : the four classic arguments against direct
realism , are all in favour of sense-data. Sense data from
different senses correlate. Sense data are beyond my
control (unlike dreams)
In favour : Locke’s examples of primary qualities are the
building blocks of modern physics .Primary qualities
resemble the objects themselves.
One warm hand and one cold hand in the same water…
In favour : the inseparability of primary and secondary
qualities ; the lack of evidence for a material substratum ;
the difference between sense-data and physical reality ;
the master argument
In favour : an argument in favour of idealism. All our
experience is of secondary qualities. Eg size can only be
perceived through changes of colour/touch
In favour : an argument in favour of idealism. We only ever
experience individual objects – we never experience the
material substratum itself.
In favour : an argument in favour of idealism. Sense data
are fleeting, private, infallible. Physical objects are
enduring, public, fallible.
In favour : an argument in favour of idealism. It seems like
a very generous offer of Berkeley. If you conceive of it, then
I will grant it. But you can’t : because by conceiving it you
entertain it within the mind!
In favour : an argument against idealism – there must be a
material substratum to explain how objects exists when
we do not perceive them
In favour : an argument against idealism. If we a pencil that
is crooked in water, is it actually crooked?
Against : the argument from perceptual variation, from time-lag, from
illusion and from hallucination
Against : although different percipients see different things, there are
privileged perspectives which can be agreed upon : eg colour under full
lighting conditions.
Against : perceiving objects directly does not mean that we perceive them
RIGHT NOW and simultaneously. We directly perceive what happened in
the recent past
Against : illusions only occur occasionally. Direct realists might argue
that most perception is direct.
Against : hallucination and dreams involve our brain malfunctioning and
creating sense-data. They occur without the veridical perception giving
us direct experience of reality. The disjunctivist theory of perception.
Against : dependence on the medium of sense-data separates us from the
physical world –prompting us to doubt the existence of the external
world. Solipsism as a possible consequence.
How can sense data represent the physical world? The two things being
compared are so fundamentally different.
Against : Berkeley argues that secondary qualities are not in the object,
but in the mind of the observer. And that primary qualities are only
accessible through secondary qualities. Also primary qualities are
relative (eg size to a flea v size to a city planner)
Against : reductio ad absurdum – without God, idealism is forced to
concede that unperceived objects vanish.
And it is not clear how we can have independent perspectives if we are
ideas in God’s mind.
Against : a blind person can conceive of the size of something. We can
logically conceive of size (the amount of water displaced by a balloon in
bowl of water) without referring to sense data.
Against : Berkeley ‘s alternative (being aspects of God’s mind) is no easier
than a material substratum to perceive/conceive of.
Against : sense data and physical objects are different, but one still
represents the other.
Against : Berkeley conflates the thought of something with what the
thought is about. We can conceive of objects that are outside the mind –
but we cannot imagine them without bringing them inside the mind. The
largest crater on the dark side of the moon?
Against : Berkeley claims that the unity and complexity of our
experiences justify belief in the existence of God. And God’s mind is the
mental substratum which unifies our experience
Against : Berkeley claims that hallucinations are ‘dim irregular and
confused’, and not coherently connected with the rest of our experience.