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Roderick Firth, Sense Data and the Percept
Theory, 1949-50.
PART I THE PHENOMENOLOGICAL BASIS OF THE
PERCEPT THEORY
1. THE NATURE OF SENSE-DATA
(a) The Definition of "Sense Datum"
To understand the position of those who reject
the Sense-datum Theory in favour of the Percept
Theory, it is necessary to consider, at least
briefly, the manner in which the term "sense-
datum" is customarily defined. It must
be recognised, first of all, that in order
to define this term philosophers have always
found it necessary to refer to a certain
kind of perception or awareness. Sometimes,
for example, sense-data are defined as the
objects of direct perception or of immediate
perception. Thus at the outset of Berkeley's
Three Dialogues, Philonous defines what he
calls "sensible things" as "those
only which are immediately perceived by sense"2
Broad defines sensa as objects of which we
are "directly aware" in a perceptual
situation".3 Price defines sense-data
as those things "directly present to
consciousness" in perception. 4 And
Moore defines sense-data as the objects of
"direct apprehension", citing as
an example of such apprehension the having
of an after-image. 5 If, however, a philosopher
wishes to speak without contradiction of
unsensed sense-data, he may define sense-data
as entities which could be directly or immediately
observed. And if he wants to distinguish
between a sense-datum and sense-field, he
may define sense-data as the distinguishable
parts of whatever could be observed in this
manner. But in any case he makes some reference
to a particular kind of observation or awareness,
which he usually describes as "direct"
or "immediate".
This does not mean, of course, that sense-data
cannot be defined without using the word
"observation" or the word "awareness";
in fact some philosophers are content to
define sense-data as entities which are (or
could be) sensed, or even as entities given
to sense, and these definitions are merely
verbal analyses of the term "sense-datum".
The important point is simply that sense-data
are defined not by an enumeration of their
kinds but rather by reference to the manner
in which we become conscious of them. We
do not say that sense-data are patches of
colour, rough things and smooth things, hot
things and cold things, etc., for we could
never be sure of exhausting the denotation
of "sense- datum" in this way.
Moreover, according to some theories, the
surfaces of physical objects can likewise
be described as "patches of colour",
"rough", "smooth", etc.,
and the question whether or not some sense-data
are surfaces of physical objects should not
be prejudiced or confused by our definitions.
Sense-data must be defined, therefore, by
reference to the manner in which we become
conscious of them: they are what we feel,
sense, intuit, or immediately observe, or
they are what is given to us, or what we
are directly aware of, in perception. And
once we understand the meaning of "sense-data"
as so defined, we can presumably decide to
some extent by empirical observation just
what kinds of entities are properly called
"sense-data".
(b) The Denotation of "Sense-Datum"
Nevertheless -- and here we come to a matter
of the greatest importance in understanding
and evaluating criticisms of the Sense-datum
Theory -- philosophers have always found
it impossible to explain the meaning of such
terms as "direct awareness" and
"immediate perception" without
mentioning at least a few examples of the
objects of such awareness or perception,
namely, sense-data. This fact has been noticed
and emphasised by Ayer and Moore. In The
Foundations of Empirical Knowledge, Ayer
points out that the terms "direct awareness"
and "sense-datum" are correlative
and that "since each of them is being
used in a special, technical sense, it is
not satisfactory merely to define one in
terms of the other". "In order
to show how one or the other of them is to
be understood", therefore, it is necessary
to use some other method of definition, "such
as the method of giving examples".6
Moore makes the same point. That special
sense of the word "see", he says,
"which is the visual variety of what
Berkeley called 'direct perception' . . .
can only be explained by giving examples
of cases where 'see' is used in that sense"7
It follows, therefore, that in order to understand
what philosophers mean by the term "sense-datum",
we must supplement our analysis of whatever
explicit statements they may have made on
the subject, by a careful examination of
the examples which they have given.
Now such an examination of the examples which
contemporary philosophers have given to illustrate
the meaning of the words "sense-datum"
and "direct awareness", will make
it quite clear that all of them who are using
these words in anything like the traditional
way, are in agreement on two important points.
They agree, in the first place, that the
sense-data directly observable by any one
sense are quite limited in their qualities.
With respect to visual perception, for example,
they agree with Berkeley that it is false
to say that "we immediately perceive
by sight anything beside light, and colours,
and figures".8 Thus our sense-datum
when we look at a dog, according to Russell,
is "a canoid patch of colour".9
And when we look at a penny stamp, according
to Broad, our sensum is "a red patch
of approximately square shape''.10 And when
we look at an apple, according to Lewis,
what is given is a "round, ruddy . .
. somewhat''.11 And when we look at a tomato,
according to Price, our sense-datum is "a
red patch of a round and somewhat bully shape".12
Thus it seems to be agreed by all these philosophers
that when we gaze, for example, from a warm
room at a distant, snow-capped mountain,
our awareness of whiteness may properly be
described as "direct", whereas
our awareness of coldness may not. One of
our sense-data is a white patch shaped like
a mountain peak but our sensation of temperature,
if we are aware of any at all, is one of
warmth rather than coldness. In colloquial
English, to be sure, we might say that the
mountain "looks cold" or "appears
cold", just as we might say that it
"looks white" or "appears
white", but such language is generally
supposed to be unsatisfactory for theory
of knowledge because it obscures the fact
that the manner in which we are conscious
of whiteness in such a case is very different
from the manner in which we are conscious
of coldness. The distinction in question
is the very one that has traditionally been
drawn by the use of such pairs of words as
"impression" and "idea",
"sensation" and "perception",
"the given" and "the conceptual",
"sense-datum" and "image",
etc., and philosophers who use the term "direct
awareness" in the traditional way must
agree, therefore that the sense-data directly
observable by any one sense are quite limited
in their qualities.
In the second place, all philosophers who
use the term "direct awareness"
in the traditional way will agree on a still
more important point, viz, that we are never
directly aware of physical objects. It may
seem, on first thought, that philosophers
who accept the theory of perception called
"direct realism", or some other
more or less sophisticated variation of naive
realism, are exceptions to this rule. Closer
examination of their positions will probably
show, however, that what these philosophers
actually maintain is that some visual and
tactual sense-data -- though not, of course,
data of the other senses -- are literally
the surfaces of physical objects. But these
"surfaces" it should be noted,
are not themselves physical objects: they
are surfaces, and differ from physical objects
in that they do not occupy a volume of space.
And since these direct realists admit that
it is only the surfaces of physical objects
which we can perceive directly (i. e., that
our sense-data are surfaces and not physical
objects) we may conclude that their theory
is not distinguished by any special propositions
concerning the psychology of perception.
To emphasize the fact that physical objects
are not accessible to direct observation,
it has long been customary among philosophers
and psychologists to reserve the verb "to
perceive" for those cases in which the
observation in question is not direct. According
to this convention, which I shall adopt,
the observing of physical objects is called
"perceiving". Thus this second
point of agreement among philosophers who
use the correlative terms "sense-datum"
and "direct awareness" in their
traditional meanings, may be stated as follows:
Physical objects are perceived but they are
never the objects of direct awareness.
(c) Criticism of the Traditional Concept
Now in view of the necessity for defining
the term "sense-datum" by the method
of giving examples, it is clear that not
only the truth but the very meaningfulness
of the traditional Sense-datum Theory depends
on the possibility of making the distinctions
involved in these two points of agreement
just formulated. Yet it is precisely these
distinctions which have been denied by philosophers
who accept the Percept Theory. They have
sometimes developed their criticism in a
rather haphazard manner, but I believe that
their rejection of the Sense-datum Theory
has always been based on objections to one
or both of these two points of agreement.
The first objection consists in denying that
there is any discoverable kind of observation
or awareness which is present in every perception,
and which takes as its objects only the kinds
of things which have traditionally been offered
as examples of sense-data. And this is not
a trivial objection, for most advocates of
the Percept Theory would go so far as to
say that the experience of a man looking
at a distant mountain from a warm room might
comprise both whiteness and coldness, each
in precisely the same manner, and neither
in any other manner -- a statement which,
as I have pointed out, has been either explicitly
or implicitly denied by all philosophers
who use the term "sense-datum"
in its traditional meaning.
The second objection to the Sense-datum Theory
is one which is not entailed by the first
but which many psychologists and philosophers
regard as an essential part of the Percept
Theory. This objection consists in maintaining
that in fact physical objects themselves
are observed as directly as patches of colour,
odours, tastes, and other so-called "sense-data".
The direct and immediate experience of anyone
who looks at the world about him, according
to this interpretation of the Percept Theory,
always consists of a number of full-bodied
physical objects. And this, of course, is
flatly to deny the distinction between perception
and direct awareness which is essential to
the Sense- datum Theory.
Now even the first of these two objections,
if valid, is sufficient to necessitate a
reformulation of most of the epistemological
theories in the history of modern philosophy.
Just how radical that reformulation would
have to be, is a question which I shall discuss
later. But the second objection to the Sense-
datum Theory has implications which are even
more serious, especially for those theories
which maintain that physical objects are
all, in some more or less literal sense,
"composed of" sense-data (or of
possible sense-data). Not only Berkeley and
other subjectivists, but many more modern
philosophers including Bergson, James, Russell,
the new realists and many of the pragmatists
and logical positivists, have supported the
view that physical objects are knowable just
because they are reducible to objects of
direct awareness. But if sense-data are defined
as the objects of direct awareness, and if,
as some advocates of the Percept Theory have
maintained, the objects of direct awareness
may be physical objects, then physical objects
are merely a subclass of sense-data. And
the theory that physical objects are in some
sense "composed of" sense-data
is either false or tautological, of course,
if it is understood that physical objects
are themselves sense-data.
In recent years, moreover, the view that
physical objects can be observed as directly
as the entities which have traditionally
been called "sense-data", has been
used by a number of philosophers as a basis
for criticizing one or more of these very
epistemological positions. Wild, for example,
has maintained in an article entitled "The
Concept of the Given in Contemporary Philosophy",
that what is actually given in perception
is a "world of things". He quotes
with approval a statement of Lewis that "it
is indeed the thick experience of the world
of things . . . which constitutes the datum
for philosophical reflection", that
"we do not see patches of colour, but
trees and houses; we hear not indescribable
sounds, but voices and violins". But
then he goes on to criticize Lewis for abandoning
this "classic view of the given"
for the more restricted one of Berkeley and
other modern empiricists. Modern empiricism,
Wild asserts, "abandons the aim of classic
philosophy to describe the thick experience
of the world of things as it is given. Instead
of this, it singles out a certain portion
of the given as peculiarly accessible or
given in some special sense". 13
Reichenbach, in his Experience and Prediction,
has also declared that physical objects are
immediately given in perception and has used
this as an argument against positivistic
theories of "reduction". Reichenbach's
position, however, is much more extreme than
Wild's. According to Wild, those things that
are called "sense-data" by modern
epistemologists are part of what is given;
what he objects to is the view that "the
immediately given alone is given". According
to Reichenbach, however, such sense-data
(what he calls "impressions") are
not given at all. "What I observe",
he says "are things, not impressions.
I see tables, and houses, and thermometers,
and trees, and men, and the sun, and many
other things in the sphere of crude physical
objects; but I have never seen my impressions
of these things".14
Many statements of this kind have appeared
in philosophical literature in recent years,
and in most cases they appear to be based
on the Percept Theory. The central thesis
of this theory now seems to be accepted by
most psychologists who are interested in
the phenomenology of perception, although
there are, as we shall see, differences of
opinion concerning the implications of the
theory. The central thesis was stated by
William James in his Principles of Psychology
as concisely, I believe, as it has ever been
stated. A perception, he said, "is one
state of mind or nothing"; if does not
contain a sensation.
"We certainly ought not to say what
is usually said by psychologists, and treat
the perception as a sum of distinct psychic
entities, the present sensation namely, plus
a lot of images from the past, all 'integrated'
together in a way impossible to describe.
The perception is one state of mind or nothing."15
We may look at a physical object in such
a way, James admitted, that what we apprehend
approaches "sensational nudity";
thus by turning a painting upside down, or
looking at it with a purely aesthetic attitude,
"we lose much of its meaning, but, to
compensate for the loss, we feel more freshly
the value of the mere tints and shadings,
and become aware of the lack of purely sensible
harmony or balance that it may show".16
Nevertheless, the fact remains that sensations
do not occur as constituents of perceptions,
but at most only as complete and independent
states of mind.
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Notes
2 Berkeley, Three Dialogues, in Works, Oxford,
1891, Vol. I, p. 381.
3 C. D. Broad, Scientific Thought, p. 239,
Kegan Paul, London, 1923.
4 H. H. Price, Perception, p. 3, McBride,
New York, 1933.
5 G. E. Moore, Philosophical Studies, p.
173 et seq., Harcourt Brace, New York, 1922,
and "A Reply to My Critics", The
Philosophy of G. E. Moore, p. 629, Northwestern
U. Press, Chicago, 1942.
6 A. J. Ayer, The Foundations of Empirical
Knowledge, p. 61, Macmillan, New York, 1940.
7 "A Reply to My Critics", in Philosophy
of G. E. Moore, p. 628.
8 Principles, in Works, vol. I, p. 282.
9 Bertrand Russell, Inquiry into Meaning
and Truth, p. 174, Norton, New York 1940.
Quine has pointed out that Russell's word
"canoid" means not "dog-shaped"
but "basket-shaped". (Review of
Russell's Inquiry into Meaning and Truth,
p 10 Scientific Thought, p. 119
11 C. I. Lewis, Mind and the World-Order,
p. 119, Scribners, New York, 1929.
12 Perception, p. 3. We may overlook for
the moment the disagreement among these philosophers
concerning the number of spatial dimensions
possessed by visual sense-data.
13 Ja.
13 John Wild, Philosophy and Phenomenological
Research, pp. 70-71, September, 1940.
14 Hans Reichenbach, Experience and Prediction,
p. 164, U. of Chicago Press, Chicago, 1938.
It is interesting to observe that in The
Unity of Science, Kegan Paul, London,
1934, pp. 45-48, Carnap himself had questioned
what Reichenbach calls "the positivist
dogma" that impressions are given. There
is a view, Carnap said, that "material
things are elements of the given", and
although "it is not often held to-day,
it is . . . more plausible than it appears
and deserves more detailed investigation".
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