From D.W. Hamlyn: The Theory of Knowledge
Perception:
When we say that we cannot properly be said to see something if it does not exist, the statement
is made against the background of certain criteria of truth for the perceptual claims in question that are
applicable to statements about ordinary objects under ordinary conditions of evidence. . .The
conventions involved in speaking of stars, of people on T.V,, or the cinema, and the consequent criteria
of truth for the peceptual claims in question, are different from those involved in speaking of seeing
ordinary things in unproblematical conditions. --- The fact that there are conditions under which alone
perception can take place in no way implies that we do not perceive a world independent of ourselves,
and that we do not often see it rightly.
The assumption behind the sense data talk is that in order to have knowledge of the world we
start from sense experiences, which must be essentially private, and somehow move from them to
knowledge of a public world independent of ourselves. Put in these terms it is an obvious problem how
this result is to be achieved. As Austin says, Ayer, despite disclaimers, is fully in the tradition of British
empiricists for whom the basically existing things and the basic objects of knowledge were ideas,
impressions or sensations. The position involves both an ontological claim and an epistemological claim,
both a claim about what fundamentally exists and a claim about what is the basic object of knowledge. ...
Wittgenstein’s arguments that language depends on rules, and the notion of a rule depends for its
application on the possibility of public checks. . .Given this general argument, the private meaning of
sensations would be feasible only within an already established public language, since that language
provides a means of giving sense to the words we use; we would come to sensation with an already
established concept of sensation, which would bring with it criteria of identity. As Wittgenstein states it:
the inner process stands in need of outward criteria. Anyway of speaking of sensations must be postperceptual --- it must, if it is to be intelligible, depend upon a prior conception and recognition of a
public world open to perception. . .
There is no possible way of building up a public world from immediately given sensations. . . The
information supposedly given in sensations would not be intelligible unless we already know what it was
like to perceive a public world. . . . Thus, Wittgenstein’s argument is a reduction ad absurdum of the
whole notion of the intelligibility of sense data. . . . One of the crucial facts about perception is that it is
concept dependent, in the sense that we cannot be said to perceive anything unless we have the concept
of the object of perception as an object independent of ourselves, unless we understand what it is for
something to be an object of this kind. --That a sense datum statement may in a certain sense be seen as more basic than a material object
statement (in that a lesser claim is made) does not mean that the notion of sense datum is basic in any
absolute sense. If one defines, as Ayer does, a sense datum as an appearance of an object, then our
understanding of the notion of sense datum presupposes and is founded upon our understanding of that
of a physical object, and this prevents sense datum from serving as any kind of foundation of knowledge.
G.A. Paul has objected to sense data theory by noting that we use the expressions “appear,”
“appearance,” “seems” only where there is doubt as to whether we are really seeing what we think we
are or where we wish to deny this. H.P. Grice responds that what he calls the doubt and denial condition
need not be fulfilled if the locution involving “seems,” “appears,” etc. is to be meaningful. But even if
one can give a successful paraphrase of the statements about sense data in terms of statements with the
terms “seems,” “appears,” etc., this will not enable a philosopher to use the notion of sense datum as a
foundation for the philosophy of perception, if he presupposes as it must, the notion of a physical object
in identifying for us the relevant appearance. . . The notion of a sense datum elucidated in this way will
not do the work that it has traditionally been intended to do. . .
Apart from idealistic theories that have stressed the rule of judgement in perception, sometimes to the
exclusion of the merely sensory, most philosophical theories have assumed some notion like that of a
sense datum and have gone on to discuss how knowledge of a world of permanent and independent
objects is built upon it. --(1) The causal theory and (2) phenomenalism are mainly theories about the nature of objects of
perception.
With (1) it is held that material objects are literally material, and that they cause impressions in us or
cause us to sense sense data. With (2), one starts from the other end and argues that the so-called
material objects are really constructs out of sense data. To a large extent (2) is a reaction to (1), since (1)
seems to imply the knotty problem of things-in-themselves. The idea that something is in principle
unknowable is a very difficult one.
Against (1): although it may be said that in some sense or other perceiving X has as a necessary
condition that X cause one to have certain experience, there are other necessary conditions of perceiving
X such as, that we must already have the relevant concepts. It is very dubious, then, that our being
caused by objects to have certain experiences could be a sufficient condition of our perception of those
objects, which is what the causal theory seems to imply.
Phenomenalism: Against (2): The main objections are that it makes “actualities” depend on possibilities
and that it has the consequences that any analysis of a material object statement will be infinitely long
and thus incapable of being carried out even in principle. . . . Both theories treat the link between
ourselves and the world as a contingent one, and thus, as a link that cannot be proved to exist. ..
The truth is that if we take appearances as somehow basic and ‘given’, hope on that basis to forge a link
with an objective world, it must be a forlorn hope. . . There is no way in which belief in an external
world can be justified or even made intelligible once we are committed to the idea that what primarily
exists are sense appeaances and that it is up to us to show how we can go beyond them.
The idealist, e.g. Bradley, is right to point out the role that concepts play in perception. It is not
right, however, to say that all perceptions involve judgement. Perceptual judgement is comparatively
rare. . . it is impossible to accept the idea that we are “given” something in sense experience, and on this
basis build up a world independent of sense experience. It is equally impossible to accept the idea that all
we mean by this world is something about sense experience. On the other hand, we are clearly not
“given” the world ready-made in perception; each of us has to learn how things are, and we have to see
them very much as others see them, even if we may sometimes differ over details. The objectivity of
perceptual judgments does not, however, consist simply in this agreement with others. . . .
If agreement does not constitute the essence of objectivity, it is at some point a necessary condition of
our giving any content to the notion of objectivity. . . . To talk of the possibility of agreement in our
perceptions presupposes a common framework, even a common world. . . The problem, thus, is one of
the relationship of sense experience to that common, independent world, the existence of which is a
precondition of the very intelligibility of discourse itself. Perception must provide a basis for objective
claims about the world. If the relationship between perception and how the world is were merely a
contingent one, perception could provide no such basis. . . if the relationship between perception and the
world were merely contingent, it would make sense to suppose that what we all see as, e.g., red, is not
red at all. . . But to suppose that any anything we count as red in any circumstance whatever is not so
would be to rob the concept of redness of any point of application. . . Thus, to suppose that what we all
see as red is not so would make sense only if there were really no understanding of what redness is at all.
Our understanding of such a concept implies that the original supposition would not make sense, and
thus that there is not merely a contingent relationship between perception and the world, between how
we see things and how they are. . . .
There are certain concepts that have perceptual criteria; they get a sense only through their connection
with perception, and it is perception under normal conditions that provides the point of application for
these concepts. . . .The necessary connection between perception and the properties of things, between
how we see things and how they are, holds only in some cases. But these cases are sufficient to
constitute points of application for other concepts, and in a sense from a foundation for our
understanding of the world, though not in a way presupposed by traditional empiricism. .. . Once we are
allowed to have perception at all, we must be allowed to have some conception of, and some awareness
of our public world, so that there is no longer any void between us and the world. . . The crucial point is
that perception is basically an awareness of an object. . . .. a view of the world is developed through
learning, because we have experiences, and because we have the capacity to develop concepts and apply
them in accordance with the framework that we are in effect taught through our relations and
communications with human beings. . ....it is this framework that provides the possility of giving
application o the concepts of knowledge and belief, and it is only in terms of it that we can speak of such
things.