Transcript A Brief and Incomplete History of the Philosophy of Science

A Brief and Incomplete
History of the
Philosophy of Science
Based largely on John Losee (1993) A Historical Introduction to
the Philosophy of Science. Oxford: Oxford UP.
Plato
(427 - 347 BCE)
• Plato’s epistemology denigrated scientific
knowledge (knowledge of natural and
material regularities)—such knowledge
was not of the true reality, but merely of
“shadows in the cave”
• Most important for Plato was knowledge
of the Forms, the abstract entities which
define the moral and metaphysical
structure of the universe
• Knowledge of the Forms was to be
gained not via observation and
inference, but through pure reason and
philosophical discourse
Aristotle
(384-322 BCE)
Inductive-Deductive Model:
General Principles
(1) Induction
Deduction (2)
Observed Phenomena
From observations one proceeds by inductive inference (1) to
General Principles which explain the observations in virtue of
the fact that those same observations can be deduced (2)
from the principles
Aristotle’s I-D Model
• Induction: enumeration, direct intuition
• Deduction: categorical logic
• Aristotle required that the General Principles be
at least as evident as the observations—
ultimately, they should be self-evident or
necessary truths
– The motivation here is to avoid arriving at claims which
describe only accidental regularities
– Rather GPs should be self-evident necessary truths
reflecting the essences of objects and relations in nature
• This is related to the issue of the nature of laws
– The problem is that it is hard to see how we can get to
necessary truths via induction
• This can be seen as an outcropping of the problem of
induction
Aristotle’s Four Causes
• Material Cause: substance which undergoes a process
• Formal Cause: general conditions required for, and pattern
or form of, process
• Efficient Cause: immediate conditions which precipitate
the process or bring the object into being
• Final Cause: the purpose or end for which the process
occurs—x occurs in order that… this sort of explanation is
called teleological
– To fully explain a phenomena, each of its four causes must be
explained
– Whereas now we focus primarily on a combination of the first
three and often try to eliminate teleological explanation,
Aristotle saw the final cause/teleological explanation as most
important to understanding the nature of things
• this raises the issue of the nature of laws and causation
Pythagoreanism
• Pythagoreans revered numbers and mathematical
relations to the point of mysticism
• The real is the mathematical patterns and harmonies
discoverable in nature
• Describe the mathematical structure of a phenomena and
you have knowledge of its essence
• This contrasts with Aristotelianism in that it focuses on the
formal cause to the exclusion of the others, it especially
neglects final causes
• Our current mathematical physics is, indeed, quite
Pythagorean
• Pythagoreanism resembles Platonism in that it gives pride
of place to abstract entities (numbers) and their relations,
but it does not have much to say about moral Forms
Pythagoreanism—Problems…
• Given their knowledge of the Pythagorean Theorem, and
the fact that they conceived of all numbers as ratios,
certain quantities were thought to be mysterious and
incommensurable (immeasurable or unable to be compared
with known quantities, what we would call the irrational
numbers), e.g.,
• Of course, any good mysticism has to have mysteries…
• A further problem is that the same phenomena can be
described by various different, but observationally
equivalent, mathematical models
• This is the issue of underdetermination of theory by evidence
• This puts in question the ideal that mathematical
description gets at the true nature of things…
Pythagoreanism and Saving
Appearances
• The tension between Pythagoreanism and the
possibility of observationally equivalent
mathematical descriptions was especially acute in
astronomy
• It was well known—e.g., by Ptolemy
(100-178)—that motion of the planets
could be equally well accounted for by
various mathematical models
• The question then becomes whether
to view mathematical description as
revealing underlying nature or as
merely providing a convenient description of the
observable phenomena (saving the appearances)
– This leads to the issue of the observation/theory
distinction and realism/anti-realism
Three Models of Planetary Motion
P
epicycle
c
a
Heliocentric
Circles
Moving
Eccentric
Epicycle/Deferent
eccentric
b
P
P
E
c
E
E
S
deferent
Planet P revolves around
point c, while c revolves
around Earth, E
Planet P revolves around
point c, while c revolves
around Earth, E
When P passes through a
and b, P will appear to
move backwards against
the night sky seen from E
(retrograde motion of P)
When c and P are on
opposite sides of E
retrograde motion of P
occurs
Planet P and Earth, E, both
revolve around Sun, S
When E passes P
retrograde motion of P
occurs
These models also account for variations in speed and distance relative to E. Further epicycles, eccentrics,
deferents, and equants can be added for greater precision. Of course, none of these is correct…
Saving Appearances
• Especially in astronomy, a tradition evolved of
not claiming reality for the mathematical
models—the task for the astronomer is not to
hypothesize about the unobservable nature of
things, but to provide convenient and
observationally adequate models
• This is a form of anti-realism
• Relates to the observation/theory distinction
• This is very similar to naive positivism,
operationalism, and current constructive
empiricism
• Ptolemy was inconsistent on this issue, usually
stressing Pythagorean realism, but sometimes
weakening his claims to saving the appearances
(though he never considered heliocentrism
plausible)
Saving Appearances…
and Oneself
• The famous heliocentrists, Copernicus (14731543), Galileo (1564-1642), and Kepler (15711630), each had Pythagorean commitments
– each held to the reality of his model, and
– each was strongly motivated, not just by data and
observation, but also by strong mathematical
aesthetics, a desire to find certain kinds of harmonies
in nature
Copernicus
• This raises the issues of scientific revolutions and the
rationality of theory change
• Yet each of the heliocentrists was advised to
present his work as a mere saving of appearances
to avoid persecution from the Church. Galileo did
not take great pains to hide his commitment to the
reality of heliocentrism. As a result, Galileo was
brought before the Inquisition and forced to
recant, spending the his last eight years under
house arrest.
Galileo
• Again, the issues of rationality, revolutions, and social
forces
Kepler
Atomism
• A further metaphysical/explanatory picture that can be
contrasted to Pythagoreanism and Aristotelianism is
Atomism
• Proponents included Leucippus (490-430 BCE) and
Democritus (460-360 BCE)
• The general approach was to explain observed qualitative
and quantitative changes by reference to quantitative
changes at a more elementary level of organization
• This, too, neglects the Final Cause, and is thoroughly
materialistic, thus it is antithetical both to Aristotelianism
and to Platonism/Pythagoreanism
• One difficulty is to avoid simply attributing to the atoms the
very property to be explained at the macro level. Doing so
would create a circular “explanation”, which is to say, no
explanation at all (e.g., day-old coffee is bitter because it
has acquired large numbers of bitter atoms)
• This raises the issue of the nature and quality of scientific
explanation as well as the observation/theory distinction
Development of the I-D model
in the Middle Ages
• The Middle Ages saw a number of
modifications to and developments of
Aristotle’s basic I-D model…
Robert Grosseteste
(c. 1168-1253)
• Attempted to systematize choice among
competing theories
– Use Modus Tollens to eliminate all but one possible
hypothesis
– I.e., deduce a consequence, C, from a hypothesis, H,
show that not-C, conclude not-H
– Modus Tollens:
If H, then C
not-C
not-H
– Problem is, this cannot be done;
it is not possible to eliminate all
but one hypothesis
• underdetermination
Roger Bacon
•
(1214-92)
Three Prerogatives of Experimental Science:
1. From general principles deduce claims about new
phenomena, and put these to experimental test
(Aristotle required only that the original
phenomena be deduced)
2. Actively and systematically experiment in order to
increase data and knowledge of phenomena
3. Use this knowledge to develop new techniques for
gathering data and testing hypotheses, as well as
for developing practical tools and new crafts; look
to old craft traditions as a source of data and
technical knowledge
•
These constitute advances over Aristotle’s simple
inductive-deductive method, because it stresses
systematic gathering of data, the extension of implications
and tests to new phenomena, and a bridging of the gap
between intellectual knowledge and craft knowledge
Scotus and Ockham on Induction
• Further forms of induction articulated
Duns Scotus
(1265-1308)
William of
Ockham
(1280-1349)
Method of Agreement
Case
Circumstances Effect
1
ABCD
e
2
ACE
e
3
ABEF
e
4
ACD
e
Conclusion
A can be the cause of e
Method of Difference
Case
Circumstances Effect
1
ABC
e
2
BC
-
Conclusion
A can be the cause of e
– These two methods are often called the (first two) of Mill’s Methods,
after J.S. Mill (1806-73), whose arguments in favor of inductivism were
widely influential.
Ockham’s Razor
• William of Ockham—Ockham’s Razor
– A demand for simplicity, stated in various forms:
• Assume nature takes the simplest path available
• assume the minimum number of (types of) objects necessary to the
theory/explanation
• do not unnecessarily complicate theory
• eliminate superfluous concepts.
• Ockham would not like the first formulation because it makes a
metaphysical claim about nature (that it pursues the simplest
path), and, Ockham would say, we cannot know how God has
designed nature—God could complicate nature unnecessarily if he
so chose
• Instead, Ockham cast his injunction so as to apply to our theories
rather than to nature itself—keep the theories as simple as
possible
– while in principle God could complicate things, we should not pretend
to knowledge of God’s design
– we should make our theories as simple and tractable as possible,
given the evidence
Necessary Truth of First Principles
•
Note that Ockham’s caution in stating his razor, as well as the cautious form of the
conclusions in the two inductive methods above, point out a growing recognition of
the fallibility of inductive inference, as well as a reconsideration of Aristotle’s
requirement that the First (General) Principles be self-evident. For some thinkers
self-evidence may still have been a goal, but many began to recognize (in theory if
not in practice) that one had to be more cautious about the strength of one’s
inductively generated conclusions.
•
Duns Scotus believed that sense experience allowed us to recognize necessary
truths, but that such truths were true in virtue of the meanings of the terms, and it
was understanding of these meanings, not sense experience, which justifies our
belief in them (see Herschel); such truths are necessary, as their denials are selfcontradictory
–
An early version of analyticity
•
Aristotle, Scotus, and others had assumed that certain first principles of the special
sciences could be known to be necessary, hence what counted as self-contradictory
extended beyond just what could be reduced to a logical contradiction
•
Nicolas of Autrecourt (c. 1300-1350+) had a much stricter notion of necessary truth,
restricting it to claims whose denials are logical contradictions
–
Much like David Hume (1711-1776) four centuries later, Nicolas concluded that we can have
no certain knowledge of causal relations (Hume also draws stronger conclusions)
–
Much unlike Hume, Nicolas used his critique to encourage faith in a Christian God
–
The issue of laws and causation
Galileo and Francis Bacon
• Galileo (1564-1642) stresses the role of
abstraction and idealization in the inductive stage
• Takes to heart and implements R. Bacon’s
injunction to test hypotheses against new
phenomena
• Is a master of qualitative observation and
experimental design
• And, of course, one of the first the use the
telescope to make astronomical observations
• Francis Bacon (1561-1626) tries to develop a more
systematic and more careful version of Aristotle’s
I-D model
– Eliminate all prejudices and assumptions
– Gather a huge amount of data and generalize
cautiously
– Build up to ultimate generalities through a hierarchy
of intermediate steps (restricted generalities)
– Science should be an organized community endeavor
– Science should have practical results, eventually man
should regain his dominion over nature
René Descartes
(1596-1650)
• Rejects Aristotelian I-D Model, and inverts F. Bacon’s ascent
to generality
– Rather than inductively building from
observations to successively more general and
more fundamental truths (as F. Bacon),
Descartes proposed to start with the most
general and most certain truths and derive more
specific knowledge and observations from those
– Clarity and distinctness a guide to a priori
knowledge of concepts, their implications, and
their application
• E.g., Descartes thought he could derive, a priori,
laws of physical matter from metaphysical truths
about extension and motion of bodies, and general
truths about the relation between mind and body
from truths about the different substances…
– Observation has a role in determining under
which circumstances regularities occur, but
observation cannot support general laws
Isaac Newton
(1642-1727)
• Advances an I-D model and an Axiomatic Method
–
Method of Analysis and Synthesis; a form
of the I-D model, but also
–
A three stage, non-inductive procedure
1. Formulate an axiom system of definitions
and relations (e.g., his laws of motion)
2. Specify a procedure for correlating
theorems deduced from the axioms with
observable phenomena (i.e., interpret the
axiom system; e.g., generalizations
concerning planetary motion)
3. Attempt to confirm the observational
implications of the system (e.g., specific
predictions concerning planetary motion)
–
Newton recognized a form of imaginative,
abstractive, and idealizing induction in
formulating the axiom system in stage 1
David Hume
(1711-76)
• Broad empiricist attack on metaphysics and causal
knowledge
– Criterion of meaningfulness
• A thought is genuinely meaningful only if it can be
traced back its constituent sensory impressions
– (similar to 20th c. positivism)
– Knowledge divided into…
• Relations of ideas
– Their denials are logically contradictory, so they
are necessary truths, known with certainty
– Subject matter restricted to logic, math, geometry—
no question of existence or causation is a relation of
ideas (see analyticity)
• Matters of Fact
– Neither a MOF nor its denial is logically contradictory,
so each is possible
– Based in knowledge of cause and effect, which is not
certain… In fact,
David Hume
(1711-76)
• Induction, Causation, Matters of Fact
– Knowledge of MOF based in knowledge of cause and
effect
– Knowledge of cause and effect based on experience
– All knowledge based on experience presupposes the
fundamental inductive principle that the future will be
like the past
– But this principle is not a relation of ideas, so it must be
a MOF…
– But then the fundamental principle of induction cannot
be justified—any attempt to do so would require
presupposing that very principle
• This is Hume’s version of the problem of
induction
David Hume
(1711-76)
• Hume concludes that our judgments concerning matters of fact
(including causal relations) are not rationally grounded at all
• Rather there are (stronger or weaker) habits of expectation which
evolve in us as a result of (i) our natural propensities and
(ii) observation of constant conjunctions of events (fire then heat,
fire then heat…)
• This “skeptical solution” is a form of psychological naturalism—
description of what we do, how we cannot avoid it
• He is rejecting inductive justification (though not inductive
practice), as well as intuition of necessary truth
• Indeed, we cannot know the “hidden springs and principles”
underlying the world we observe, all we ever “know” of is the
constant conjunctions of kinds of events—laws and causation
• Except, perhaps, for Nicolas of Autrecourt, Hume is the first we’ve
looked at to completely reject the ideal of somehow arriving at
secure generalizations or certain First Principles of some sort
• Hume, unlike Nicolas, used these skeptical results to argue
against metaphysics and religion
Immanuel Kant
(1724-1804)
• Kant responds to Hume by distinguishing the form
from the content of knowledge
• Form is not given in experience; rather the “raw
data” of experience is structured in various ways
by the rational human mind
– Space and Time are the Forms of Sensory Intuition,
all perception is structured by these forms
– Perceptions so structured are further organized and
synthesized according to 12 Categories of
Understanding (e.g., Unity, Substance, Causality, Contingency, etc.)
– Judgments are made and organized via the Regulative Principles of
Reason
• Since the structures/forms Kant posits are inherent in the human
rational mind, they are open to philosophical investigation, they
can be known via pure reason
• Since any knowledge (esp., empirical/scientific) presupposes the
Forms, Categories, and Principles, we can (contra Hume) have
knowledge of the general features of any possible scientific theory,
including fundamental and general truths about causation, matter,
motion, etc.
Immanuel Kant
• Transcendental Idealism
from a point of view which attempts to transcend our forms of
cognition, we recognize how much our mind and its structure
contributes to our knowledge of the world
• Empirical Realism
from a point of view which does not attempt the impossible
transcendence, the structures imparted by the Forms, Categories,
and Principles are fully real, and necessary truths regarding such
things as causal relations and matter can be known
• Some problems with this ingenious and seductive picture:
– What justifies saying “this is what any theory or cognition must
presuppose”? How can we be sure we’ve correctly identified the most
basic forms, categories, and principles? Must they be unique? Kant
thought he had identified unique basic forms, but some of what he
took as basic to science has since been changed and rejected by
science
– How can one coherently speak of the transcendental unreality of forms
and categories, while maintaining that transcendence is impossible,
and that the transcendental (noumenal) world is unknowable?
J.S. Mill
(1806-73)
• Laws, General Principles, and theoretical
claims are justified by inferences from
experience which satisfy inductive schemas
or forms—this is known as Inductivism
– Much like the I-D model, but little import
allowed to the D side, and Mill had very
specific inductive methods in mind
• Mill a bit unrealistic about how well
inductive schemas can justify theoretical claims
• Deduction from hypotheses of successful prediction a
requirement, but not a justifying factor unless all other
possible hypotheses are eliminated
• Again, justification of theoretical claims is gained only by
conformity of the data to inductive schemas supporting the
theoretical claims…
Mill’s Methods
Method of Agreement*
Method of Difference*
Method of Concomitant Variation
Case
Circumstances
Effect
1
A·n BC
a·n b
2
A·0 BC
a·0 b
3
A·1/n BC
a·1/n b
Conclusion
(occurrence of a is varying proportionally
to occurrence of A)
So either A causes a, or A and a have a
common third cause
Method of Residues
Case
Circumstances
Effect
1
ABC
2
B
b
3
C
c
Conclusion
abc
*See Scotus and Ockham on Induction
A is the cause of a
Hypothetico-Deductivism
• William Whewell (1794-1866) and
W.S. Jevons (1832-82) rejected Inductivism
• Rather than justified on the basis of
inductions, a hypothesis is justified when it
– Is consistent with other established
hypotheses, and
– The consequences deducible from the
hypothesis agree with observations
Whewell
• With its strong emphasis on predictive test,
this is in the spirit of Aristotle, R. Bacon,
Galileo, and Newton, but the view gives
more priority to predictive test than these
others (by giving much less importance to
induction)
Jevons
Herschel on Discovery and Justification
• John Herschel (1792-1871)
• Herschel distinguished the issue of how a
theory was arrived at (context of discovery)
from the issue of its acceptability or
justification (context of justification)
• He claimed that context of discovery is
strictly irrelevant to context of justification
• Discovery
– Use of inductive schemas
– Abstraction and imaginative hypothesis
– F. Bacon-like hierarchy of generalizations
• Justification
– Success of deduced predictions (thus a form of hypotheticodeductivism), especially
• Extension of predictions to extreme cases
• Deduction of unexpected predictions and their successful testing
• Use of “crucial experiments” to decide between competing
theories/hypotheses
Problem(s) of Induction
• Two Issues:
– The Descriptive Issue: we arrive at beliefs regarding unobserved
matters of fact (future particulars, eternal generalizations)—How do
we do that?
– The Normative Issue: do we arrive at such beliefs the way in which
we ought to arrive at them? I.e., are we justified in our practice? If not
is there any practice we could adopt which is justified?
• Problems Regarding the Normative Issue:
– Uncertainty/Underdetermination : Inductive inference is
underdetermined, hence not truth-preserving, hence some amount of
uncertainty is involved, even when starting from certain premises
– Lack of Rational Ground: The basic principle(s) of induction are not
logical truths, nor self-evident, so what justifies those principles? As
Hume points out, we cannot appeal to experience, because any such
appeal presupposes the very inductive principles in question—this is
the problem
• A useful online discussion: The Problem of Induction
Underdetermination
• The Underdetermination of Theory by Evidence
• Given any amount of observational evidence, there will be more
than one (indeed infinitely many) theories compatible with that
evidence
• A unique theory is never dictated by the evidence, not even if we
had all possible evidence
• This raises the question of how and if we can rationally decide
between theories
• WRONG and often WRONGLY ATTRIBUTED TO W.V. Quine version:
a theory can be preserved in the face of any contrary evidence
(what Quine says, in case you’re interested, is that a hypothesis
or statement can be preserved as long as others are given up, but
this is a CHANGE IN THEORY, some hypotheses are preserved,
others not)
– This correct understanding of Quine implies that
• There are no crucial experiments to rule out a hypothesis
• There are (near) crucial experiments to rule out whole theories
Observation/Theory
Distinction
• Intuitively, there seems to be a distinction between that which we
can observe—the observational; and that which we cannot
observe—the theoretical
– Observable: people, stars, trees, rocks, grains of sand, a patch of
red…
– Theoretical: electrons, quarks, viruses, dark matter, the big bang,
trees, people…
• The theoretical is posited or inferred to help predict and explain
the observable
• Problems abound for this distinction:
– Does the distinction concern observable vs. theoretical
• Objects?
• Words and Sentences involved in scientific claims?
• Sense Data vs. Things in the World?
– How sharp is the distinction?
• Does something projected onto the retina through a microscope or telescope
count as observable?
• What about artificially colored images produced on a screen by an electron
microscope or an infrared sensitive telescope?
• What about “observations” made by a prosthetically enhanced human?
Revolutions and Rationality
• Given the problems of Induction and
Underdetermination, is theory acceptance
(change) at all rational?
• If so, there must be some substantial
constraints on theory acceptance beyond
mere induction and deduction of
observable consequences
• What are they? How do we know?
next slide…
Revolutions and Rationality
• Kuhn claims that scientific revolutions (periods of significant
change in theory and practice) are highly non-rational affairs,
highly unconstrained
• In part, this is because what makes a revolution revolutionary is
that the normally accepted theories and the methodological
practices they ground are in question and changing, hence, it
seems, they cannot constrain their own change in a rational way
• But revolutions are lauded as important advances in our thinking
and knowledge, and we think they are good and justified changes
in theory—but how could they be if they are not rationally guided?
• Moreover, historians of science often recognize that many social
forces can play a role in revolutions and the (non)acceptance of
theory—what gives?
• Finally, the apparent lack of rational constraint and presence of
social forces raise the demarcation issue—how, if at all, is science
different from other organized bodies of beliefs (religion,
metaphysics, political structures, cultural tradition)?
Social Forces
• How and to what extent do religious, cultural,
political, gender, racial biases and interests affect
scientific theorizing?
• Can they be avoided? Ought they to be avoided?
• This has implications for the issue of the
rationality of theory acceptance and change
• If theory acceptance and change are not
rationally constrained there seems to be plenty of
room for non-rational social forces to be in play
• Moreover, the apparent lack of rational constraint
and the role of social forces raises the
demarcation issue…
Demarcation
• How, if at all, is science different from other
organized bodies of beliefs (religion,
metaphysics, political structures, cultural
tradition)?
• How can a difference be marked out?
• Can “good” science be distinguished from “bad”
science? Is “pseudoscience” a third thing, or just
really bad “bad” science?
• Does/should science have a privileged
epistemological standing in relation to these
others?
• This all relevant to revolutions and rationality,
and social forces
Realism/Anti-realism
• Given the various epistemological difficulties
(underdetermination, problem of induction,
rationality, social forces), and the lack of a
consensus on these issues, why should we think
that our theories are actually describing reality?
• The apparently large gap between observational
and theoretical knowledge inspires worry about
realism
• Metaphysical difficulties come into play here as
well—we do not have good understandings of the
nature of laws and causation, explanation, so
how can we claim that we are discovering the
nature of the universe?
Laws and Causation
• Laws are often thought of as general statements of causally
necessary connection between events, and the statements
of laws themselves are sometimes thought to be necessary
truths
• But given the various epistemological problems, especially
the Humean critique, it is unclear whether or not causes
and laws can be or be known to be as described above
• If laws do not state a necessary connection and are not
themselves necessary truths, then what, if anything,
distinguishes them from accidentally true generalizations?
• Is there really any such thing as a law of nature?
• This all connected to issues of realism and explanation
Explanation
• Science is supposed to explain things to
us…
• But what does it mean to have a scientific
explanation?
• Does mere derivability of a description
from more general truths constitute an
explanation?
• What sort of explanations can science
provide?
• How can we tell good from bad
explanations?
Analyticity
•
•
Statements which are analytic are supposed to be conceptual truths—true in virtue of
the meanings or concepts involved
–
Locke: a part of a complex idea is predicated of the whole
–
Kant: the predicate concept is contained in the subject concept
–
Carnap: true in virtue of the meanings of the constituent terms
–
E.g., ‘all bachelors are unmarried’
This is contrasted with synthetic statements whose truth (or falsehood) is a matter of
something beyond the meanings or concepts involved (the world, matters of fact)
–
E.g., ‘all faculty are bachelors’
•
Locke and Kant were the first to make use of this distinction, it played a prominent
role for the logical positivists (as we’ll soon see), Quine repudiated it
•
Analyticity provides a way (though not the only way) of explaining how at least some
truths are
–
Knowable a priori—without appeal to experience—via linguistic analysis or merely
understanding the language
–
General principles, or frameworks, for theorizing
–
Necessarily true
–
A matter of linguistic convention
–
Accepted or rejected on purely pragmatic considerations and thus lack metaphysical import
it all depends on who is making the distinction and to what use they are putting it