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Philosophy 226f: Philosophy of Science

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Title: Philosophy 226f: Philosophy of Science


1
Philosophy 226f Philosophy of Science Prof.
Robert DiSalle (rdisalle_at_uwo.ca) Talbot College
408, 519-661-2111 x85763 Course Website
http//instruct.uwo.ca/philosophy/226f/
2
Common ideas about scientific method Inductivism
Science proceeds by performing experiments
repeatedly, and accumulating observations. Then
it makes inductive generalizations from the
accumulated facts. These are the laws of science.
(Francis Bacon) Hypothetico-Deductivism Science
proceeds by devising hypothetical models for how
nature might really be organized. Then it deduces
the consequences of these models, and compares
them with observation. (cf. The mechanical
philosophy)
3
The Newtonian method of experimental
philosophy Instead of making up theories to
explain the facts, find ways to make the
phenomena answer the important theoretical
questions. Example Use the laws of motion to
impose questions on the world, such as, what
forces are at work? If the laws are assumed to
be true, then every acceleration that we see is
telling us something about a force. Perturbation
theory Any departure from ideal Keplerian motion
in the solar system indicates-- and is a measure
of-- the action of a yet-unaccounted-for force,
whose source is a yet-unaccounted-for mass.
4
Phenomenal measures of theoretical
magnitudes Centrifugal forces as measures of
rotational velocity Keplerian harmonic law Ta2
/ Tb2 Ra3 / Rb3 measures the variation of the
interplanetary force as 1/R2. Stability of the
planetary orbits also measures the force
law. Agreeing measures of the same magnitude by
different phenomena provide the best possible
evidence.
5
Example Mercurys perihelion precession measures
the force to be 1/R2.00000016.
But this disagrees with the measure provided by
the other planets, whose orbits are too stable.
6
All of this reasoning from phenomena
presupposes the laws of motion. Therefore the
laws of motion cant be the products of such
reasoning. But what is the status of the laws of
motion? Inductive generalizations? Deductive
consequences of more basic principles? A priori
assumptions of some kind?
7
Kantian questions about scientific method How
has science achieved universal assent, while
philosophy is the subject of endless
dispute? What distinguishes scientific reasoning
from philosophical reasoning, so that the former
leads to principles that are necessary and
universal, whereas the latter remains arbitrary
and particular? How can philosophy start on the
secure path of a science?
Immanuel Kant, 1722-1804
8
Kants Copernican Revolution The laws of
nature dont describe the way things are in
themselves they describe conditions that our
understanding imposes upon experience. Every
effect has a cause is not a truth about things
in themselves. If it were, we would be right to
doubt it. Instead, it is a rule that the human
understanding imposes on the appearances, in
order to submit them to a rule. Without such
rules experience would be impossible. The world
would be a chaos of sensory appearances.
9
Kant Scientists like Galileo comprehended that
reason has insight only into that which it
produces itself after a plan of its own...for
otherwise, accidental observations, wth no
previously fixed plan, will never be made to
yield a necessary law. Reason, holding in one
had its principlesand in the other hand the
experiments it has devised according to those
principles, must approach nature in order to be
taught by it. It must not, however, do so in the
manner of a pupil, who agrees to everything the
teacher says, but of an appointe judge, who
compels the witness to answer the questions which
he himself has phrased
10
Newtons laws as synthetic a priori principles A
priori Known prior to experience A posteriori
Known by experience only Analytic propositions
True by definition the predicate belongs to the
definition of the subject Synthetic propositions
Joining a new predicate to the subject, one not
contained in its definition Newtons laws
represent the law of causality as applied to the
entire universe.
11
Jules Henri Poincaré (1854 -1912)
If the laws of motion were inductive, they would
be easier to revise. If they were synthetic a
priori, they would be impossible to arrive. We
would not be able to conceive of
alternatives. They must be another kind of
principle altogether.
12
A triangle whose internal angles sum to something
less than two right angles
13
Triangle whose angles sum to more than two right
angles
14
Parallel postulate Given a line L and a point P
not on L, there is exactly one line through P
that does not intersect L.
P
L
T
Equivalently, if lines L1 and L2 cross a line T,
L1 and L2 will meet on that side of T where their
internal angles with T are less than two right
angles.
L1
L2
15
On a saddle surface, there may be infinitely many
lines through P that do not intersect L.
P
L
16
On a spherical surface, every line (great
circle) through P will intersect L.
P
L
17
Poincaré Where do the fundamental principles of
geometry get their appearance of certainty? How
is it that they seem to be universal and
necessary, and yet applicable to the real
world? Einstein To the extent that the
principles of geometry apply to reality, they are
uncertain to the extent that they are certain,
they dont apply to reality. Could we ever be
required to modify them in the face of experience?
18
Poincaré How do we interpret experience in which
triangles seem non-Euclidean?
19
What is a non-Euclidean experience? An
experience in which straight lines behave as the
straightest lines of a non-Euclidean space. But
what is a straight line? The path of a light
ray. So, how do we distinguish between these two
possible interpretations of our experience? The
geometry of space is non-Euclidean. OR
Something is happening which prevents light from
propagating in straight lines.
20
Poincaré The two pictures of spatial geometry
represent two ways of saying the same thing. What
we measure is only the displacements of the
physical objects that we use in measurement. The
results of those measurements are open to a
number of possible interpretations. The choice
between such interpretations is a matter of
convention. Is Euclids geometry true?
According to Poincaré, the question has no
meaning. As well ask whether the metric system is
true.
21
The fundamental laws of physics and physical
geometry are not synthetic a priori
principles. They are not a priori, since
alternatives are possible. They are not
synthetic, but are principles of a peculiar kind
they appear to describe the real world, but in
fact they only enunciate criteria for the
description of the world. Newtons law of
inertia is not a description of nature, but a
criterion that we adopt in order to be able to
measure physical forces. It cant be contradicted
by the facts, since it is the principle by which
we investigate the facts. Such principles are
definitions in disguise.
22
The hierarchy of science, according to
Poincaré Every science presupposes more basic
sciences, as part of the language in which it is
written. Those are a priori with respect to
that particular science. Logic is presupposed by
arithmetic. Arithmetic is presupposed by
geometry. Geometry is presupposed by
physics. Therefore physics cant proceed until a
geometry is fixed by convention. Physics cant,
in turn, force us to revise geometry.
23
Pierre Duhem There are no unrevisable principles
in physics. Every principle is, in effect, an
empirical hypothesis. Holism An empirical test
is always a test of all the principles that are
presupposed in the test. In chemistry, we can
keep the theory out of the laboratory. But in
physics, experiments always presuppose a great
deal of theory. When an experiment gives the
wrong result, there is no certain way to decide
which principle is at fault.
24
Ernst Mach Phenomenalism Everything that is
real is some combination of phenomenal elements
apparent to some observer. The human mind imposes
order and regularity among these elements by
identifying large collections of phenomena--even
infinite collections of possible phenomena--
under particular concepts. This tendency exhibits
the principle of mental economy to comprehend
experience with the least possible expenditure of
mental effort. This is an adaptive feature of
humans as products of evolution.
25
  • Replacing experience by the reproduction of
    facts in thought
  • Knowledge of general rules replaces the effort of
    understanding countless individual cases.
  • Systematic rules substitute for the experience of
    new cases scientific knowledge provides us with
    a vicarious experience of evolutionary trial and
    error.
  • Our theories venture into situations in which
    ourselves would be at some risk.

26
Implications regarding scientific theories
Laws of nature should not be thought of in the
traditional way, as identifying powers or
forces or mechanisms underlying the
phenomena. Instead, laws simply describe, in
the most economical manner possible, the
functional dependencies that exist among various
phenomena. Example It is unscientific to speak,
following Newton, of determining the true
motions. Force is proportional to acceleration
relative to the fixed stars.
27
  • The Darwinian theory Evolution by natural
    selection
  • (Blind variation and selective retention)
  • Inherited structural features of all living
    things are subject to random variation.
  • Some variations will be more useful than others
    for survival in a given environment, and will
    increase an organisms chance of surviving and
    reproducing.
  • Any environment will have limited resources to
    support living populations, while organisms will
    tend to reproduce beyond what those resources
    will support.
  • There must be a struggle for existence which will
    select variations for survival and inheritance.

28
Observations supporting Darwins view 1.
Geological patterns reveal the earth to be much
older than previously thought, old enough for
gradual processes (like natural selection) to
have tremendous effects. 2. Fossil record
indicates that numerous variations have existed
and become extinct, and that many present species
have ancestral forms. 3. Artificial selection in
domesticated species reveals the same basic
processes at work. 4. Different animal and plant
species arise from very slight variations on a
few basic structures. 5. Differentiation reflects
differences in environmental pressures, among
forms that are isolated from one another.
29
Darwins empirical premises That gradations in
the perfection of any organ or instinct, which we
may consider, either do now exist or could have
existed, each good of its kind that all organs
and instincts are, in ever so slight a degree,
variable that there is a struggle for existence
leading to the preservation of each profitable
deviation of structure or instinct.
30
. It is so easy to hide our ignorance under such
expressions as the plan of creation, unity of
design, c., and to think that we give an
explanation when we only restate a fact. Any one
whose disposition leads him to attach more weight
to unexplained difficulties than to the
explanation of a certain number of facts will
certainly reject my theory.
31
It is interesting to contemplate an entangled
bank, clothed with many plants of many kinds,
with birds singing on the bushes, with various
insects flitting about, and with worms crawling
through the damp earth, and to reflect that these
elaborately constructed forms, so different from
each other, and dependent on each other in so
complex a manner, have all been produced by laws
acting around us.
32
Darwins fundamental laws Growth with
Reproduction inheritance which is almost
implied by reproduction Variability from the
indirect and direct action of the external
conditions of life, and from use and disuse a
Ratio of Increase so high as to lead to a
Struggle for Life, and as a consequence to
Natural Selection, entailing Divergence of
Character and the Extinction of less-improved
forms.
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