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Duhem's
Philosophy of Science
The Aim of Science
Duhem's statement of the aim of science is
similar to Mach`s: the aim of science is economy of
thought. Like
Mach, Duhem believes that experimental laws
contribute an intellectual economy, because they
summarize a large number of concrete facts.
But unlike Mach, Duhem furthermore says that
theories also contribute to the realization of the
aim of science.
The economy achieved by the substitution of a
law for concrete facts is redoubled for the mind,
when the mind substitutes theories for the numerous
experimental laws.
A theory is a system of mathematical
propositions deduced from a small number of
principles, which aim to represent as simply, as
completely, and as exactly as possible, a set of
experimental laws.
Its aim in other words is economy of thought
by schematically representing and logically
organizing experimental laws.
Scientific
Criticism
Duhem developed a sophisticated theory of
scientific criticism, and it is central to his
philosophy of science.
He is very emphatic in defending the autonomy
of empirical science from any encroachment by
metaphysics or natural philosophy.
Metaphysics pertains to realities that
underlie the phenomenal appearances that are hidden
by the phenomena, while science pertains to these
appearances. Consequently
whatever may be the criteria and procedures for
criticizing a metaphysical thesis, they are not
relevant to empirical science.
In empirical sciences that are
nonmathematical, the generalizations such as
"all men are mortal" may be accepted or
rejected as simply true or false.
But in mathematical physics the equations
both of the empirical laws and of the hypothetical
theories are not simply regarded as true or false,
but are approximate.
The amount of indeterminacy due to the
approximate nature of the values of the variables in
these equations will be reduced as experimental and
measurement techniques improve.
These improvements in theory occur because
instruments are improved.
And because instruments depend on physical
theory, the improvement of instruments occurs in
turn due to the improvement in theory.
As the range of this indeterminacy becomes
smaller, the equations of either the empirical laws
or the hypothetical theories that represent the laws
may no longer be able to predict values for their
variables that fall within the smaller range.
When this happens, the equations are no
longer satisfactory.
Duhem is very emphatic in his thesis that the
only criterion that may validly operate in
scientific criticism is the ability of the law or
theory to make accurate predictions.
This exclusion of all prior ontological or
metaphysical criteria from scientific criticism has
been carried forward into the contemporary
Pragmatist philosophy of science.
It shows up for example as Quine’s
rejection of all “first philosophy.”
In his theory of scientific criticism Duhem
rejected the use of so-called crucial experiments as
a means of establishing the validity of a theory.
His thesis is that if the physicist is
confronted with several alternative theories, the
rejection of all but one cannot imply the
establishment of the remaining one.
As an example he cites the two alternative
theories of light: one theory is the hypothesis that
light is a stream of high speed projectiles, and the
other is the hypothesis that light consists of
vibrations whose waves are propagated in an ether.
This is not an anticipation of the Copenhagen
duality thesis; Duhem is thinking of the wave and
particle theories as alternative theories.
His position is that the choice is not
mutually exclusive, because no one can ever
enumerate completely all of the various hypotheses,
which may pertain to a determinate group of
phenomena. He
thus maintains that several alternative theories may
fall within the range of indeterminacy of the
measurement data and experimental laws, so that more
than one theory may be satisfactory.
This represents a pluralistic thesis about
science, and in the crucial experiment discussion,
it means that even if all hypotheses could somehow
be enumerated, elimination could not leave but one
to be considered as established. More generally his pluralism means that the indeterminacy in
measurement, laws, and theories produces
indeterminacy in scientific criticism.
This pluralism is another aspect of his
philosophy of physical theory that has been carried
forward into the contemporary Pragmatist philosophy
of science.
His theory of scientific criticism also
reflects his wholistic or organic view of theories.
This wholistic view not only makes the
meanings of the mathematical symbols mutually
determined by the context consisting of the
equations of the theory, it also necessitates
testing the theory as a whole together with all the
hypotheses used in the experiment including
assumptions about the measuring instruments.
If the prediction in the test is wrong, not
only may the proposition being tested be at fault,
but also the whole theoretical scaffolding used by
the physicist.
The physicist can never subject an isolated
hypothesis to experimental test, but only a whole
group of hypotheses.
The only thing that the experiment reveals is
that among all the theoretical propositions used to
predict the phenomenon, there is at least one error.
Thus the failure of the prediction does not
inform the physicist where the error lies or reveal
which hypothesis should be modified.
In Duhem's view physics is not like a machine
which lets itself be disassembled; the physicist
cannot test each piece in isolation and then make
adjustments to the isolated part found wanting.
Duhem compares physics to an organism in
which one part cannot be made to function except
when the parts that are most remote from it are
called into play.
When there is a malfunction felt in the
organism, the physician must ferret out through its
effects on the entire system, the organ that needs
to be remedied or modified without the possibility
of isolating the organ and examining it apart.
Duhem says that the physicist confronted with
a failed prediction is more like a physician than a
watchmaker.
Scientific
Discovery
Duhem also has a philosophy of scientific
discovery. Unlike
Mach's view on discovery and invention in science,
Duhem's is not principally a theory of perception.
He anticipates later philosophers including
the Logical Positivists with his emphasis on the
language of science.
For him scientific discovery is not reduced
to noticing what had previously been overlooked in
perception; for him discovery is also the
construction of theoretical hypotheses.
The construction of a theory involves four
successive operations: Firstly certain physical
properties are taken as simple, so that other things
are combinations of these simple properties.
These properties are not simple in any
absolute sense like Mach's elements, but are taken
as simple for purposes of the theory only.
The simple properties are measured, and the
magnitudes are assigned to symbolic variables.
Secondly the magnitudes are connected by
propositions that are hypotheses, and that serve as
postulates of the deductive system.
Thirdly the postulates are not realistic or
phenomenalist, but are freely created; using them
requires only that the logic of algebra be correctly
applied for making deductions.
Fourthly the conclusions drawn from the
postulates are compared with the experimental laws
that the theory is intended to represent.
If the conclusions agree with the laws within
the degree of approximation corresponding to the
measurements taken in the experiments, then the
theory is said to be a good theory.
Such acceptable theory may in turn be used
for the further development of measuring instruments
used in experiments, as well as constituting the
final product of the scientific endeavor with its
maximum economy.
Improved theory produces improved
instruments, which in turn produce better
measurements. These
better measurements reduce the range of the
indeterminacy in the numerical data, which may cause
the theories to fail in their predictions.
This failure will occasion two types of
responses. The
initial response is to modify the theory with
corrections, which will enable the predictions made
with the theory to fall within the smaller range of
indeterminacy produced with improved measurements.
But these corrections also complicate the
theory, and in due course "good sense" may
lead some physicists to decide to refrain from
adding more complicating corrections, and instead
attempt to revise the hypothetical postulates of the
symbolic schema, the whole theory itself.
The accomplishment of such a revision is the
work of the genius.
But Duhem does not subscribe to the heroic
concept of invention; history creates the genius as
much as the genius creates history.
The physicist does not choose the hypotheses
on which he will build a new theory; the theory
germinates within him.
This germination is not sufficiently
explained by the contemplation of the experimental
laws that the theory must represent.
It is a larger cultural development.
In due course when the cultural process that
he calls universal science has prepared minds
sufficiently to receive a theory, it arises in a
nearly inevitable manner.
Often physicists who do not know one another
and who are working great distances from one
another, generate the same theory at the same time.
In the course of his studies the historian of
science according to Duhem often observes this
simultaneous emergence of the same theory in
countries far from one another.
Scientific Explanation
On Duhem’s philosophy theories do not
explain the laws nor do the laws explain the facts. Explanation is proper only to metaphysics and not to science.
In the opening sentence of the introduction
to his Aim and
Structure of Physical Theory,
Duhem says that he offers a simple logical analysis
of the method by which physical science makes
progress. While
affirming the autonomy of physics with his thesis
that agreement with experiment is the sole criterion
of truth for a physical theory, Duhem has a
distinctive concept of scientific progress, which he
elaborates in the appendices to the book.
He says that there are two types of
development in physics that are occurring
simultaneously.
One is what today would be called the
revolutionary type of development consisting of a
succession of alternative theories, in which one
theory arises, dominates the scene for the moment,
and then collapses to be replaced by another theory. The other is an evolutionary progress in which constantly
more ample and more precise mathematical
representation of the phenomenal world is disclosed
by experiment.
When the progress of experimental science
goes counter to a theory and compels the theory to
be modified or transformed, the purely
representative part enters nearly whole into the new
theory, bringing to it the inheritance of all the
valuable possessions of the old theory, while the
hypothetical part falls away in order to give way to
another theory.
The first type is identified with the
mechanistic physical systems including Newtonian
physics as well as Cartesian and atomic physics.
The second type is identified with general
thermodynamics, which Duhem believes will lead
physical theory toward its goal.
He envisioned this goal as the convergence
toward an analogy with Aristotle's physics.
He concludes in his discussion of the value
of theory, that the physicist is compelled to
recognize that it would be unreasonable to work for
the progress of physical theory, if theory were not
the increasingly better defined and more precise
reflection of a metaphysics.
He thus concludes his book with the thesis
that belief in an order transcending physics is the
metaphysical justification of physical theory.
Duhem's History of Physics
Just as Mach had written a history of physics
viewed through the lenses of his philosophy of
science, so too did Duhem.
However, Duhem's effort was relatively
monumental; it is a work originally intended to be
twelve volumes of which ten were actually written
before its author's death in September 1916.
This magnum opus was his System of
the World: A History of Cosmological Doctrines from
Plato to Copernicus.
The central thesis of this work is summarized
in a much smaller book begun earlier, To Save the Phenomena: An Essay on the Idea of Physical Theory from
Plato to Galileo (1908).
The thesis is that the hypotheses of physics
and especially the heliocentric hypothesis in
astronomy are mere mathematical contrivances for the
purpose of saving the phenomena.
Pope Urban VIII condemned Galileo in 1633 for
maintaining that Copernicus' heliocentric theory is
not merely a mathematical contrivance, but is rather
a description of the real world.
Formerly Cardinal Bellarmine, the Pope
maintained that regardless of how numerous and exact
may be the confirmations of a theory by experience,
these confirmations can never transform a hypothesis
into a certain truth that can be taken
realistically, since this transformation would
require that the experimental facts should
contradict any other hypotheses that might be
conceived, a requirement that cannot logically be
satisfied. Galileo,
on the other hand, maintained that because
Copernicus's theory saved the phenomena more
adequately than any alternative hypothesis, the
Copernican theory had to be a realistic one.
Contemporary Pragmatists agree with Duhem's
rejection of any prior ontological criteria for the
criticism of scientific theory, but contrary to
Duhem they furthermore agree with Galileo's practice
of scientific realism.
Contemporary Pragmatists are realists, who
let the most empirically adequate theory decide the
ontology. Galileo's
argument for realism is the same as Quine's doctrine
of ontological relativity, and Feyerabend calls it
the Galileo-Einstein tradition of realism.
And Heisenberg invoked this tradition, when
he referenced Einstein's realistic interpretation of
relativistic time in the relativity theory, and then
used it as a precedent for his own realistic
interpretation of the quantum theory's duality
thesis, notwithstanding Bohr's instrumentalist
complementarity principle.
Duhem, however, denied that science is
realistic, and he construed Galileo's argument as a
case of the fallacy of the crucial experiment.
He argued that it is impossible to enunciate
all the possible hypotheses, and establish the truth
of one by elimination of all others.
The accomplishment that Duhem credits to
Kepler and Galileo is the rejection of Aristotle's
view that celestial and terrestrial physics are
fundamentally different, and that hypotheses of
physics must save all the phenomena of the inanimate
world.
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NOTE: Pages do not
corresponds with the actual pages from the book
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