ppt file - UC Davis

The Problems of Philosophy
Philosophy 1
Spring, 2002
G. J. Mattey
Bertrand Russell
Born 1872
From England
Anti-war activist
Won Nobel Prize for
literature (1950)
• Author of popular
• Died 1970
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.
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
• No two people see and feel it the same way
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
Two Questions
• Is there a real table at all?
• If there is a real table, what are its real
• Both are very difficult to answer
• Sense-data are things immediately known in
• 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 sensedatum
• The sense-data are not the table or properties of
the table, so how are they related to the table?
• 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
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
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?
• 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
• 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 sensedata
• It also accounts for behavior such as that of a cat’s
exhibiting hunger
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”
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
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
• Private shapes differ when public shapes are static
• 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
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
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
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
• The intrinsic properties cannot be known through
the senses
• It is gratuitous to think that any sense-data
resemble properties of physical objects
• 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
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
• 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
• 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
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
Knowledge by Description
• We know things by description as “the soand-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
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
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-andso”
• When we know an object by description, we know
it as “the so-and-so”
• Definite descriptions imply existence and
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