University of Zurich, Philosophical Seminar
Fall semester 2018
Seminar “Bertrand Russell: Probleme der Philosophie”
Lecturer: Prof. Dr. Christoph Emanuel Viebahn
The difference between real and imaginary sense-data
in Russell’s The Problems of Philosophy
Delivery date:
27.02.2019
Number of characters: 24’612
Riccardo Fornera
Sihlfeldstrasse 55
8003 Zurich
079 948 63 79
riccardo.fornera@uzh.ch
Matriculation number: 18-702-746
Summary
1. Introduction ............................................................................................................. 3
2. Main part ................................................................................................................. 4
2.1
Sense-data ......................................................................................................... 4
2.2
The existence of the external world .................................................................. 6
2.3
Sensation and imagination ................................................................................ 8
3. Conclusion............................................................................................................. 12
4. Bibliography .......................................................................................................... 12
2
1. Introduction
Many philosophers have tried to describe the external world and our knowledge of it. A large part of
them have used the concept of “sense-data” to do that: sense-data give us real knowledge of the world
we live in and the things we interact with, as many have said. But what about things we can’t directly
perceive, like imaginary objects? Are the sense-data derived from them real too?
The main target of this seminar paper is to clarify the difference (when there is one) between real
sense-data and imaginary sense-data as described by Bertrand Russell in his works and what he means
with these terms, in order to become more acquainted with our knowledge of what is real and what is
not.
First of all I will have to define what sense-data are, how we deal with them and what Russell thinks
about them. Then I’ll talk about our knowledge of the external world, its existence and how it may
be proved. Finally I will discuss the difference between “sensation” and “imagination”, a question
which is very close to the initial target of this work.
To do all that I will start my analysis with some excerpts taken from Russell’s The Problems of
Philosophy, where the subject is only summarized. The rest of my paper takes inspiration mainly
from some consideration of two other texts written by Russell: Our Knowledge of the External World,
a series of lectures held by Russell at the Universities of Oxford and Harvard, where he explores the
issue more deeply and accurately, and Theory of Knowledge.
3
2. Main part
2.1 Sense-data
“Sense data are the alleged mind-dependent objects that we are directly aware of in perception, and
that have exactly the properties they appear to have.”1 This is the definition given by the Stanford
Encyclopedia of Philosophy (SEP) and it can be deconstructed into three primary characteristics of
sense-data that will help us to understand a bit more about them, always according to the SEP:
1)
Sense-data are the kind of thing we are directly aware of in perception,
2)
Sense-data are dependent on the mind, and
3)
Sense-data have the properties that perceptually appear to us2
Bertrand Russell focuses mainly on the first characteristic and using his simple example of the table
he shows that what we perceive is not the same as the real object (the table in this case): things as
colors, smells and sounds are called sense-data because they are immediately known in sensation, but
we cannot say that the table is the sense-data, or is composed by sense-data, or even that the sensedata are intrinsic properties of the table3.
When we interact with an object we can describe some of its characteristics to other people and they
will agree with us about them. This fact has led us to believe firmly that we all see, touch and feel the
same object, but as soon as we try to be more precise some problem arises. For instance, light affects
the way we see the object and it actually changes the color we perceive, “it follows that if several
people are looking at the table at the same moment, no two of them will see exactly the same
distribution of colors, because no two can see it from exactly the same point of view, and any change
in the point of view makes some change in the way light is reflected”4. This means that sense-data
are strictly subjective and we can never be completely sure that other people have the same sensations
as we do when interacting with an object, even if they look similar as we use language to describe
them.
A “sensation” is called by Russell the experience of being immediately aware of such things as
colors5. We can have a sensation of a color, but the color itself is not a sensation, it’s a sense-datum.
1
Huemer 2004
Ibid.
3
Russell 1912: p. 13
4
Ibid.: p. 10
5
Ibid.: p. 13
2
4
We’ll need this definition afterwards, but first we have to ask ourselves why sense-data are so
important in philosophy and why in the first place many philosophers argued (and still argue) about
them. The answer is found at the very beginning of The Problems of Philosophy, where Russell
wonders if there is “any knowledge in the world which is so certain that no reasonable man could
doubt it”6. This apparently simple question has troubled philosophers for centuries and it’s the one
that has led to the discovery of sense-data, for sense-data theorists – and Russell amongst them – have
come to the conclusion that we can at least be sure of the existence of our own sense-data. That
doesn’t necessarily mean that we can be sure of the existence of the things from which we perceive
the sense-data, but it partly answers the initial question of Russell.
Before sense-data were introduced in the philosophical debate there were actually already many
doubts on the reality of the world of senses: the Indian mysticism, the Greeks (for instance Parmenides
and Plato) and also Berkeley had criticized the appearance of the external world we are given by our
sensory organs, judging it as incomplete if not misleading from reality. Nowadays, then, science tells
us that what we perceive is made of many tiny atoms that don’t look like what we thought and have
different properties from the things of which they are part. This to say that the sensitive appearance
has been struggling with a great amount of “attacks” during the centuries and Russell himself – a
supporter of the cartesian methodological doubt – believes that we ought to admit as probable that
the immediate sensitive objects depend on our physiological conditions for their existence, although
he doesn’t think that this means they are mind-dependent7. But what Russell and many other
philosophers claim is that, however our sense-data “may depend upon us, yet their occurrence is a
sign of something existing independently of us, something differing, perhaps, completely from our
sense-data whenever we are in a suitable relation to the real table”8. The definition of the “real table”
and our relation with it will be of great relevance for the target of this paper.
In order to get close to the definition of what is real, of what exists, Russell starts – as many others
have done – from the well-known aphorism of Descartes: “cogito, ergo sum”, that means “I think,
therefore I am”, i.e. I can be absolute certain of my own existence since I doubt, since I think. But
Russell argues that even this simple sentence says rather more than is strictly certain: “When I look
at my table and see a certain brown color, what is quite certain at once is not ‘I am seeing a brown
color’ but rather, ‘a brown color is being seen’. This of course involves something (or somebody)
which (or who) sees the brown color; but it does not itself involve that more or less permanent person
6
Russell 1912: p. 9
Russell 1914: p. 80
8
Russell 1912: p. 16
7
5
whom we call ‘I’. So far as immediate certainty goes, it might be that the something which sees the
brown color is quite momentary, and not the same as the something which has some different
experience the next moment”9.
I think this argument is quite unnecessary if not fallacious. We said that we can be certain of our own
sense-data, but Russell here claims that when we perceive an object the only thing certain concerns
the sensation, not the subject having that sensation. He says that there must be a subject, yet this isn’t
necessarily us (it could be God, like Berkeley would say), but how could we be certain of our own
sense-data if we were not even certain of ourselves? It’s true that we change continuously and we are
not the same of one moment ago, but this objection, if taken seriously, would imply a major revolution
in our language, since we could not say things like “I am seeing a brown color” anymore, for it would
be impossible to do an action extended in time; and this is not the right place to do that. So I think
that this clarification is not to be believed, and I will stick with Descartes’ aphorism.
2.2 The existence of the external world
It’s now clear, I hope, that we can be certain of the existence of ourselves and of our sense-data; the
next problem is how to prove that the table, the physical object, really exists, and if its existence
depends upon us and/or our sense-data or if it’s independent. According to common sense, almost
everybody agrees that, when looking at a table, its temporary existence is out of the question, but
what happens when, for instance, it’s covered with a cloth and we can’t see it anymore is a little more
complicated. It’s logically primitive (in the sense that it’s instinctive) to believe the table will continue
to exist when not directly seen, but Russell claims that psychologically this belief is due only to the
fact that we have already seen that table before, therefore we need a concrete point to justify it10.
To do this Russell separates what he calls “hard” data from “soft” data. He means “by ‘hard’ data
those which resist the solvent influence of critical reflection, and by ‘soft’ data those which, under
the operation of this process, become to our minds more or less doubtful”11. Among the hard data we
9
Russell 1912: pp. 19-20
Russell 1914: p. 87
11
Ibid.: p. 85
10
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find for instance the particular facts of sense, and the general truths of logic, while the belief that
sensible objects continue to exist when we are not perceiving them is clearly a soft datum. This latter
sort of data is capable of logical proof, so that they then again become believed, but no longer as data.
The best we can hope, Russell claims, is that hard data may prove soft data to be at least probable12.
We can now go back to the question if the existence of the table is independent or not and generalize
it this way: “can we know of the existence of any reality which is independent of ourselves?”. As
Russell explains, “when we say that one thing is ‘independent’ of another, we may mean either that
it is logically possible for the one to exist without the other, or that there is no causal relation between
the two such that the one only occurs as the effect of the other” 13. Then he continues by saying that
the only way “in which one thing can be logically dependent upon another is when the other is part
of the one”14. So he rewords the question as “can we know of the existence of any reality of which
our Self is not part?” and concludes that the Self cannot be considered part of the immediate object
of sense15.
All these rather complicate arguments are needed to prove (or at least try to) a very simple thing, that
Russell explains with the instance of the hungry cat: “if the cat exists whether I see it or not, we can
understand from our own experience how it gets hungry between one meal and the next; but if it does
not exist when I am not seeing it, it seems odd that appetite should grow during non-existence as fast
as during existence. And if the cat consists only of sense-data, it cannot be hungry, since no hunger
but my own can be a sense-datum to me”16. This basic argument is neither exhaustive nor conclusive,
but its immediacy and the fact that it comes from an instinctive belief lead us (and Russell) to admit
that it’s safe to say that the external world does really exist, and is not wholly dependent for its
existence upon us and our continuing to perceive it. Thus sense-data are really signs of the existence
of something independent of us, inseparably bound with that something, of which they are
appearances that we can perceive17.
12
Russell 1914: p. 86
Ibid.: p. 88
14
Ibid.
15
Ibid.
16
Russell 1912: p. 23
17
Ibid.: p. 24
13
7
2.3 Sensation and imagination
For the moment we have considered only allegedly real objects and we discovered that we can be
quite certain of their existence. But what about imaginary objects, like things we perceive in a dream?
Everybody naturally feels that they are different from real objects, but as soon as we stop to reflect
about this difference we find ourselves in a rather embarrassing ignorance. Is this difference in the
object? In the sensation? In ourselves? Or in something else?
When we dream, we certainly do have the sensations we think we have, but it’s generally held that
no physical object corresponds to those sensations. We don’t realize we are dreaming until we wake
up (except for some cases of lucid dreams), so we can’t really say there’s something different in the
sensations we feel. The sense-data in a dream just do not appear to have a correspondence with such
physical objects as we should naturally infer from our sense-data18. For these reasons Russell says
that there are no such things as “illusions of sense”: we call those objects of sense unreal merely
because of the unusual and uncoherent nature of their connection with other objects of sense, for
instance, in dreams, illogical jumps across time and space are apparently normal. For every other
aspects – insists Russell – they are as real as the waking-life objects. But is this really the only
difference?19
I would like to elaborate on this subject now. First of all we can say that words like sensation and
imagination denote a two-term relationship between subject and object (by “relationship” we’re
meaning that the subject has some sort of familiarity with the other entity), and we have to find out if
they differ in the nature of their relationship or just in the nature of the object20. To do this Russell
uses the following criterion: “if we can find a case where the object is the same in two experiences
which yet differ intrinsically, then the two experiences must involve different relations to the object.
Thus if an object O can be given either in sensation or in imagination, and if the two experiences can
be seen to be different by mere inspection, without taking account of their relations to other
experiences, then we must conclude that sensation is a different relation from imagination”21. Before
trying to do that, it’s helpful to adjust our very partial definition of sensation and imagination by
excluding the memory from the picture, which also belongs to the category of experiences that we
put under the name of “familiarity”. The memory obviously has a relationship with an object that is
18
Russell 1912: p. 22
Russell 1914: pp. 97-98
20
Russell 1913: p. 127
21
Ibid.: p. 128
19
8
in the past, therefore we can define together sensation and imagination as familiarity with objects not
given as prior than the subject. This will ease our next steps a bit, avoiding complicate objections22.
To discover the differences in their relation with the object, I think is a good idea to talk about
sensation and imagination in terms of space. Different people see the same object as of different
shapes, according to their point of view (of course now we’re accepting the hypothesis that other
people exist and we can trust their witnesses, otherwise it would be too complicated), so the real shape
of the object (admitting the proof for its existence that we gave before) must be in a real space that is
public, opposed to the various apparent spaces that are private to every percipient. Physical objects
are in the real space, that for Russell is the space of science (“physical” space) 23, so the object we
perceive is only one of many variations of the physical object, which is obviously unattainable by our
senses (e.g. we cannot see an object from every possible point of view at the same time).
The sense-data we perceive are part of our private space, but our sensations are caused by physical
objects, which, as we stated, are situated in the public space. It’s clear though, according to Russell,
that “the relative positions of physical objects in physical space must more or less correspond to the
relative positions of sense-data in our private spaces”24. So, he continues, “we may assume that there
is a physical space in which physical objects have spatial relations corresponding to those which the
corresponding sense-data have in our private spaces”25. This close relationship between public und
private spaces is the main characteristic of a sensation: being undoubtedly subjective and personal,
yet similar to that of other people in more or less the same conditions (e.g. someone near us will see
a very similar table as we do).
On the other hand, what characterize the imagination is the absence of a public space accessible to
everyone. There is not the chance to compare our mental images with those of other people: if a group
of people were said to think about a horse, each person would probably think about a very different
horse. These horses would obviously be at least a bit similar to each other, but they would be much
more different from a situation in which a group of people saw the same horse and got a bunch of
sense-data from it (i.e. had a sensation).
So sensation and imagination, both private experiences, differ in their relationship with the physical
space, in the sense that in the sensation we have a tight connection to the physical object (which is in
the physical space), while in the imagination this connection is fleeting and weaker.
22
Ibid.: p. 131
Russell 1912: p. 28
24
Ibid.: p. 29
25
Ibid.: p. 30
23
9
Since we discussed the role that space plays in the sensation and in the imagination, it seems fair to
deal also with time, since it appears that space and time are always bound someway. In fact, Russell
writes: “in so far as time is constituted by duration, there is the same necessity for distinguishing a
public and a private time as there was in the case of space. But in so far as time consists in an order
of before and after, there is no need to make such a distinction; the time-order which events seem to
have is, so far as we can see, the same as the time-order which they do have”26.
However, for our analysis some sort of distinction will be needed. When we’re awake, the public and
private time are different just in our perception of the duration of a moment, but although we might
feel that certain moments pass more slowly (e.g. because we’re bored) and other pass more rapidly
(e.g. because we’re having fun) and be surprised when we realize how much time actually passed,
there are no surprises in what concerns the order of the events (at least for things happened not long
before), as Russell also claims27. He then warns us about a possible misunderstanding of the previous
argument about space: “if a regiment of men are marching along a road, the shape of the regiment
will look different from different points of view, but the men will appear arranged in the same order
from all points of view. Hence we regard the order as true also in physical space, whereas the shape
is only supposed to correspond to the physical space so far as is required for the preservation of the
order”28.
When we dream, instead, the public time is left outside, and I believe that during dreams our private
time becomes for us our real time, in the sense that as we’re inside a dream we have no external
reference point of time which anchors us to the reality, therefore everything in the dream seems to
happen exactly in the logical order of time we would expect, so we don’t feel the need to question its
authenticity and it’s the only kind of time we may refer to. Almost the same can be said when we talk
about a general form of imagination: real time doesn’t interfere with our mental images; thus we can
say that the object in the imagination is given without any specific temporal relation with the subject29.
So, in terms of time, the difference between sensation and imagination doesn’t stem from the way
time-order is given in them, since we saw that they both follow an allegedly logical line of time, rather
from the shape and structure of their time-dimension, i.e. their relation with the subject, which are
unequivocally different: in the sensation the object is given as simultaneous to the subject (when we
26
Russell 1912: p. 31
Ibid.
28
Ibid.
29
Russell 1913: p. 131
27
10
perceive something, the object and the subject are said to be on the same moment in time), while in
the imagination, as we claimed before, this relation is not specified.
Let’s focus again on the imagination to clarify a bit this idea. It’s possible for us to think about objects
that change (e.g. a plant growing up). This physical change would also imply a temporal change that
is necessary to a thing to change, but an imagined object doesn’t have a temporal position, thus it
doesn’t “need” a lapse of time to change, it can do it instantaneously. As Russell stated: “An object
imagined at one moment but not at another need not itself undergo any intrinsic change during the
time between the two moments: it may merely cease to have that relation to the subject which consists
in its being imagined. But such cessation may easily produce the belief that the object itself was at
the time when it was imagined, though, as is clear in the case of abstract object, this is in no way
implied by the change that has occurred”30. This lack of a specific temporal position is also the reason
why imagined objects are considered irrelevant for the study of physics and the other physical
sciences.
At this point we can rewrite the definitions of sensation and imagination with the additions we
discovered. “Imagination” is acquaintance with objects which are not given as having any temporal
relation to the subject and that are not in the physical space. “Sensation” is acquaintance with objects
given as simultaneous with the subject that are in the physical space. Of course Russell tries to find
also other differences between this two, but I don’t consider them of enough value to be analyzed
here, since even him is not completely convinced of what he claims.
During this analysis I’ve given for granted that dreams were to be considered a kind of imagination,
but maybe it’s good to make this clear before arriving at the end of this work. Physiologically, the
sensation is always characterized by an external stimulus that causes our mind to perceive the object,
while in the imagination this stimulus is absent and we may say it’s the will that causes our
imagination. But this point is dangerous because it would make the dreams more like a sensation,
since there is no will when we are dreaming, we are passive just like in the sensation. What convinces
us that dreams are really imagination is the realization, as soon as we wake up, of their illogical
connection to the physical reality, which makes it impossible for them to be like the sensation31.
30
31
Russell 1913: p. 132
Ibid.: pp. 136-137
11
3. Conclusion
Sense-data allow us to get to know a part of the external world, but we have to pay attention and
distinguish real sense-data from imaginary sense-data: the first ones are given to us through the
sensation, while the last ones through the imagination. The actual difference though is not much in
the sense-data themselves, rather in the connection between the object from which they are perceived
and the subject.
We discovered that imaginary objects are not considered real because of the unusual nature of their
connection with other objects of sense, but most importantly we found out that the difference between
the two kinds of sense-data can be summed up as a different relationship with real time and space of
the subject perceiving the object.
4. Bibliography
Primary sources:
-
Russell, Bertrand, Probleme der Philosophie, ger. transl. Suhrkamp 2017 (orig. ed. The
Problems of Philosophy, Williams and Norgate, London 1912)
Secondary sources:
-
Huemer, Michael, "Sense-Data", The Stanford Encyclopedia of Philosophy (Spring 2019
Edition), Edward N. Zalta (ed.), URL =
https://plato.stanford.edu/archives/spr2019/entries/sense-data/ [access on 26.02.2019]
-
Russell, Bertrand, Teoria della conoscenza, edited by Elizabeth Ramsden Eames, it. transl.
Sara Marconi, Newton Compton Editori, Roma 1996 (orig. ed. Theory of Knowledge. The
1913 Manuscript, George Allen and Unwin Ltd., London 1956)
-
Russell, Bertrand, La conoscenza del mondo esterno, it. transl. Maurizio Destro, Newton
Compton Editori 1971 (orig. ed. Our Knowledge of the External World as a Field for Scientific
Method in Philosophy, George Allen and Unwin Ltd., London 1914)
12