This document discusses Bertrand Russell's views on philosophy and knowledge. It summarizes that Russell believed we can only be directly acquainted with our sense data, but we use logic and description to infer the existence of physical objects in the world. While idealism argues that only minds and ideas exist, Russell argues for a view of logical simplicity and correspondence between sense data and an external world. We can know things through description and general principles, even if we are not directly acquainted with them.

1. The Problems of Philosophy
Philosophy 1
Spring, 2002
G. J. Mattey

2. Bertrand Russell
• Born 1872
• From England
• Aristocrat
• Anti-war activist
• Won Nobel Prize for
literature (1950)
• Author of popular
essays
• Died 1970

3. Russell’s Contributions
• Discovered, and tried to solve, “Russell’s
paradox” in the theory of sets
• Published first widely-read treatise on symbolic
logic (with A. N. Whitehead)
• Tried to reduce mathematics to logic (logicism)
• Applied symbolic logic to philosophical problems
• Co-founder of analytic philosophy (with G. E.
Moore)

4. Perceptual Relativity
• We think that our ordinary beliefs are certain, e.g.,
I am sitting at a table of a specific shape
• But these beliefs are very likely to be wrong
• We describe the table on the basis of what we see
and feel, and we think others would describe it in
the same way
• But the description only reflects our own point of
view
• No two people see and feel it the same way

5. Appearance and Reality
• A painter is concerned with appearance, a
practical person with reality
• The philosopher wants to know what appearance
and reality are
• Perceptual relativity shows that color is merely
appearance: the table has no single color
• The same considerations hold for shape, hardness
• The real table is not immediately known by sense

6. Two Questions
• Is there a real table at all?
• If there is a real table, what are its real
characteristics?
• Both are very difficult to answer

7. Sense-data
• Sense-data are things immediately known in
sensation
• Sensation is the experience of being immediately
aware of sense data
• Colors, shapes, textures are sense-data
• So, a sensation of color is the sensation of a sense-
datum
• The sense-data are not the table or properties of
the table, so how are they related to the table?

8. Idealism
• Objects such as tables are physical objects
• The collection of physical objects is matter
• Berkeley tried to show that matter does not
exist at all, and at least succeeded in
showing that its existence is not certain
• He admits that sense-data are signs of
something mental outside us
• The real table is an idea in the mind of God

9. Existential Doubt
• If we cannot be sure that matter exists, we
cannot be sure that other people exist
• We may be all that exists (solipsism)
• Even the “I” might be doubted
• All that is certain is that a sense-datum is
being perceived at a time
• This is the solid basis for knowledge

10. From Sense-Data to Matter
• Do sense-data provide good evidence that
physical objects exist?
• Common sense, on the basis of practice,
answers in the affirmative
• There must be matter for there to be public
objects that are neutral with respect to point
of view
• Why believe there are such objects?

11. Similarity
• One argument for public objects is that
there is similarity in people’s sense-data
• But this begs the question, because it
supposes that there are other people
receiving sense-data
• They may be part of my dreams
• So evidence for public objects must come
from our own private experiences

12. Simplicity
• There is no contradiction in supposing that my
private experiences have no public counterpart
• My dreams present elaborate scenes
• But it is simpler to explain my sense-data through
public objects
• The simplicity is due to the continued existence of
public objects, which accounts for gaps in sense-
data
• It also accounts for behavior such as that of a cat’s
exhibiting hunger

13. Human Behavior
• The real advantage of public objects is in
the explanation of human behavior
• Sounds and motions are produced that are
most simply explained by reference to a
body similar to my own
• Public objects can also account for dreams
• “Every principle of simplicity urges us to
adopt the natural view”

14. Belief in Physical Objects
• Our original belief in physical objects is
instinctive, not demonstrative
• It seems that the sense-datum is the independent
object (Hume)
• There is no good reason to reject the natural belief,
given its explanatory simplicity
• It is the task of philosophy to show how our
deepest instinctive beliefs form a system
• The possibility of error is diminished by the
harmony of the parts of the system

15. The Nature of Physical Objects
• Science has drifted into reducing the phenomena
of nature to motion
• The motions of physical objects are not identical
to sense-data (e.g., the light itself)
• Nor is the space we see and feel the space in
which physical objects exist
– The space we feel and the space we touch are distinct
(Berkeley)
• Private shapes differ when public shapes are static

16. Correspondence
• Physical objects cause sensation through
interaction with a physical body
• Changes in sense-data should reflect changes in
bodily position relative to objects
• The senses testify in favor of one another
• Other people confirm what we belief
• So we may assume that there is a physical space
corresponding to our private space

17. Knowledge of Physical Space
• We can know of physical space only what is
required to explain the correspondence
• For example, we can know that the moon,
earth, and sun are in a line to explain the
appearance of an eclipse
• But our knowledge is limited to relations of
distance and does not extend to distances
themselves

18. Knowledge of Time
• The private feeling of duration is a poor
guide to public durations
• But the order of public events corresponds
to that of private experiences, “so far as we
can see” (and this holds for space)
• The correspondence is not exact
– Lightning is really simultaneous with thunder
– The light we see left the sun eight minutes ago

19. Knowledge of Physical Objects
• Differences in sense-data correspond to some
differences in physical objects
• We have no direct acquaintance with the
properties in the physical objects
• We know only the relations they hold to one
another
• The intrinsic properties cannot be known through
the senses
• It is gratuitous to think that any sense-data
resemble properties of physical objects

20. Idealism
• Idealism is the doctrine that what exists (or is
known to exist) is in some sense mental
• This doctrine is absurd from the point of view of
common sense
• But we only know of public objects that they
correspond to sense-data
• We cannot reject the doctrine that the intrinsic
character of public objects is mental simply
because it is strange

21. Berkeley’s Argument for Idealism
• The existence of sense-data depends on us
• Sense-data are immediately-known ideas
• All we know immediately about common objects
(e.g., a tree) is the sense-data
• There is no reason to think that we know anything
else about them
• So the being of a tree is its being perceived
• Its public character is explained through God

22. Fallacies
• To know a tree, it must be “in” our minds, but
only as thought of
• But it does not follow that it is “in” our minds as a
private object
– When I have my wife in mind, she does not exist there
solely as a private object
• An idea exists in the mind as an act, but its object
may be “before the mind” while it exists outside
the mind

23. Acquaintance
• An argument for idealism is that what we are not
acquainted with is of no importance for us, and so
does not exist
• It is granted that we do not know in the sense of
being acquainted with matter
• But it is of importance to us
• And we can know things with which we are not
acquainted—we can know by description through
general principles

24. Knowledge of Things
• The simplest kind of knowledge of things is
by acquaintance, as with sense-data
• Knowledge of things by description requires
knowledge of truths: general principles
• Acquaintance with does not yield
knowledge of truths
– I know the color directly but I do not thereby
know any truth about the color

25. Knowledge by Description
• We know things by description as “the so-
and-so”
• The table is “the physical object which
causes such-and-such sense-data”
• To know the table, we must know general
truths about causality
• Knowledge by description rests on
knowledge by acquaintance as a foundation

26. Objects of Acquaintance
• Our knowledge would be very limited if we were
only acquainted with sense-data
• Memory extends sense-data
• We also have higher-order acquaintance with our
states of being aware (self-consciousness)
• For example, acquaintance with seeing the sun is
with the fact “Self-acquainted-with-sense-datum”
• I know that I am acquainted with this sense-datum

27. Definite Descriptions
• We are also acquainted with universals such as
whiteness, diversity, brotherhood
• This is required for the use of language
• A definite description is of the form “the so-and-
so”
• When we know an object by description, we know
it as “the so-and-so”
• Definite descriptions imply existence and
uniqueness

28. Knowledge by Description
• Descriptions can be nearer or further from
the things with which we are acquainted
• We know the things described only through
the components of a description with which
we are acquainted
• But we can use descriptions to go beyond
the limits of private experience, as in the
case of physical objects