In the third dialogue between Hylas and Philonous

the third dialogue between Hylas and Philonous there is a discussion about the
process of immediate perception. So far, Hylas understands that we can never
know what things are really like because we cannot think that sensible qualities
really resemble the true qualities of objects. Hylas is therefore worried that
we can never have access to true nature, only to the things that we perceive.
Philonous argues Hylas is wrong because he has a sceptical view depending of
the theory that real things are material and it is only once he abandons this
view, that he will no longer have a reason to be sceptical. Philonous asserts
that idealism is immune to scepticism: we cannot doubt that what we are
perceiving really exists or not because the mere fact we are perceiving it
constitutes its existence, therefore, for all sensible objects, ‘esse is percipi’ (to be is to be
perceived). “Berkeley holds that it is impossible for us to be mistaken about
the immediate objects of perception, for he holds both that immediate objects
of perception are ideas and ideas are wholly present to the mind” (Rickless, 2013). However, Hylas does
not agree that idealism can be without scepticism, he argues that even if we
can successfully reject materialism, we will never be able to replace it with a
more satisfactory theory. Therefore, Hylas sets forth a series of objections to
show that idealism cannot survive as a theory any more than materialism could.  


of Hylas’s objections regards the cases where perceptions mislead us. He claims
that Berkeley’s theory of idealism does not give an adequate account of
illusions and hallucinations. Hylas argues that since we perceive bundles of
ideas, there must be an idea that corresponds to illusions we experience;
however, we do not say that the physical object is as it looks in the illusion.
He says, for example, if we see an oar in water, it will appear bent to us. Then
if we lift the oar out of the water we will see that it is really straight thus
the bent appearance of the oar was an illusion caused by the refraction of the
water. His question is therefore, if the oar is nothing in reality over the way
it is perceived, then is it really straight or is it crooked? If we take
Philonous’s approach, we cannot say that we are wrong about our initial
judgement of the oar, because the sensible qualities really resemble the true
qualities. Therefore, it is obvious that what is immediately perceived is a crooked

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argues in response that the perceiver is not misperceiving; they are not
mistaken in regard to the data they are perceiving, instead, “the error arises in
such perceptual situation only when the perceiver makes an inference from what
has been immediately perceived.” (Stack, 1970). Therefore, Hylas is
right in that what we perceive when looking at the oar half-submerged in water
is that it is crooked, however, we are wrong in our judgement. If the perceiver
would “conclude that upon taking the oar out of the water he shall perceive the
same crookedness; or that it would affect his touch, as crooked things are wont
to do: in that he is mistaken…his mistake lies not in what he perceived immediately,
and at present (it being a manifest contradiction to suppose he should err in
respect of that) but in the wrong judgement he makes concerning the ideas he
apprehends to be connected with those immediately perceived.” (Berkeley, 1988). Therefore, the
illusion we perceive only becomes misleading if we were to infer from it that
when we touched the oar it would feel crooked or when we pulled the oar out of
the water then it would look crooked. However, Berkeley argues that in
immediate perception, there is no inference, simply the perception and
collection of the sense-data and this “indubitability of immediate perception
is one of the essential aspects of Berkeley’s theory of perception” (Stack, 1970). Berkeley does not
allow for errors in the ideas that we actually have; so, to say that ‘the oar
is crooked’ is a false statement about what ideas would be had if certain
conditions existed. Ultimately, Philonous concludes that if we were to judge
that the oar is crooked, we have made the wrong judgement because we have
inferred incorrectly about the other sensations of the oar. Therefore,
illusions mislead us regarding the ideas we might associate with what we


problem with this response is that it entails that when the oar is
half-submerged in water it is crooked because it is what we immediately perceive.
Berkeley argues that reality is the ideas that we perceive thus there can be no
distinction between appearance and reality yet, to say that the oar is both
crooked and not crooked at the same time seems very odd. In the Three
Dialogues, Berkeley does not consider or respond to this objection but in his
other writings he claims that the fundamental problem here rests with language.
He accepts that we cannot say that ‘the oar is crooked’ because this would be
claiming an oar can be straight and crooked at the same time. However, since we
can only know things as they appear to us, we cannot know what things look like
under normal conditions therefore, we can avoid the implication by claiming
that instead of the oar being both straight and crooked, we should say it ‘looks
crooked when half-submerged in water’. He claims that our language and
understanding restricts us so the reason why we say that the oar is straight
but appears crooked is because that is our understanding of the laws of nature
and what we call ‘the oar’ is just a bundle of perceptions that looks crooked
when in water.  


A more significant implication of the
objection is that it still defeats Berkeley’s idealism. Berkeley’s response
regarding language does not account for all perceptual errors for example, we
can have nightmares or hallucinations that are very vivid to the extent that we
could mistake them for reality. Key to his argument is that the ideas we have
of real things have both constancy and regularity about them and they appear to
be governed by the laws of nature. Nevertheless, illusions and hallucinations
do not fit in with our other experiences in a coherent way – when hallucinating,
my experiences stand out in comparison to my normal experiences, therefore,
Berkeley suggests that there is a larger difference between what we associate
as ‘real’ and what we associate as ‘illusory’. This explanation however still
seems inadequate, to simply say that there is a difference between the two is
not enough. It is possible that people could have dreams that resemble their ‘real’
experiences, for example, one might dream that they got a glass of water in the
middle of the night when in fact they stayed in bed. Berkeley does not account
for the possibility that illusions and hallucinations could fit in with our
everyday experiences, that they don’t always have to be hallucinations of a flying
pig, therefore, he does not fully overcome the objection that idealism cannot
give an adequate account of hallucinations and illusions.