Transcript Philosophy 2301 - Orange

Philosophy of Science
Class 7
Admin…
• Want to move my office hours tomorrow to 4:00-5:00.
If you were already planning to come between 5:30 and
6:30, let me know.
• Can you e-mail Assignments? Generally, no (class too
big!). Yes, if you are having printing problems- follow
up with a hard-copy a.s.a.p (I will do a quick compare).
• Test- 30%,30% or 20%, 40%
Review of Dates
• March 15- hand in outline/summary. You can use
the drop box (special d.b. hours)
• March 16- outline/summary pick up (office
hours),
• March 22- Final Test, outline/summary pick up
• March 29- Hand in Rough Draft
• April 2 (Friday)- pick up Rough Drafts (office)
• April 5, pick up Rough Drafts (class)
• April 8th- Final Draft Due- drop box
Quick Review of Last Class…
Good theories have…
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Testability in principle
Explanatory power
Deepens and Broadens understanding
Predicts new phenomena
(Used currently by scientists to accept or reject
theories)
August Comte and Positivism
(1798-1857)
A ‘Grown Up’ Science
• Science is limited to the observable
and therefore
• Science should stick with what it is good
at- observation and generalization!
(You can probably see that Comte was a
big fan of Bacon and Hume)
The Logical Positivists
Logical Positivists
• Do theoretical entities really exist?
• Vs
• What do theoretical terms mean?
Verificationism
• “the meaning of any statement is its method
of verification”
• My blue ball bounces
=
• If I drop this blue ball on the floor it will
rebound back upwards once it has hit the
floor
Operationalism
• Just a further refinement of verificationism…
• X is p means if O is performed on x then R
• The blue ball is bouncy
=
• The blue ball is bouncy means if I throw the blue
ball at the floor from height y and with motion x
and observe its trajectory then I will observer that
it will come immediately back up off the floor to a
height z
The Ceteris Paribus Problem
(All things being equal)
The problem of material
implication
(the if…then problem)
Truth Tables
I like dogs
I like cats
I like dogs and I
like cats
True
True
True
True
False
False
False
True
False
False
False
False
Truth Tables
Statement A Statement B Statement A and
Statement B
True
True
True
True
False
False
False
True
False
False
False
False
Happy Logicians
• Generalized from actual examples of
English
• But then defined to be true
• A nice precise system.
• Or is it?
If then statement
Statement A Statement B If Statement A
then Statement B
True
True
?
True
False
?
False
True
?
False
False
?
It is raining
True
I (will) take If it is raining
my umbrella then I (will) take
my umbrella
True
?
True
False
?
False
True
?
False
False
?
Lets check our intuitions with a poll…
(first, write down what you think)
More intuition checking…
Owls eat
mice
Ice Freezes
If Owls eat mice
then ice freezes
True
True
?
True
False
?
False
True
?
False
False
?
Some Problems…
• Particular instances don’t seem adequate to
completely verify the if then statement.
• It seems strange to put unrelated sentences
in an if then statement and give it causal
power.
• The last two lines of the truth table seem
very ad hoc and unintuitive
The logicians must make a decision…
(Studies in Logic,. Charles Pierce, 1883,Tractatus
Logico-Philosophicus- Wittgenstein, 1921)
Statement A Statement B If Statement A
then Statement B
True
True
True
False
True
False
False
True
True
False
False
True
Remember- it’s a definition!
Side note
• In case you think this is some strange
philosophical move that demonstrates the
silliness of philosophers…
• Mathematicians make moves like this in
math, too (e.g. negative numbers)…
• It is a problematic consequence of wanting
to have consistent, rigorous systems.
x is fragile = If (x is dropped on the
floor) then (x will be destroyed)
Problem:
The fragile sock problem:
A dog grabs the sock before it
can hit the floor- and eats it…
Carnap’s Correspondence Rule
Patch
• Carnap (1891-1970)
• Carnap’s patch: iff
• If O is performed on x, then (x is p iff R)
• If x is brought near the leaf microscope at
time t) then (x is (electrically charged) iff
(the leaves of the electroscope diverge).
• (Note: iff = ‘if and only if’)
Pros and Cons
• Removes the problem of Material
Implication- Yay! Definitions work again.
• The term of interest, p, is now buried:
– If O is performed on x, then (x is p iff R)
Are these really serious
problems?
• Remember:
– Philosophers want their theories to work with
logic all the time- they must be foolproof!
– Philosophy isn’t about ignoring problems
‘because they are too small’
– The logical positivists wanted their theory to be
solid and ‘nit-pick’ free.
Logical Positivism- still popular!
• Why? Well…
• Can you think of any alternatives to trying
to define theoretical terms?
• (Maybe Atomism vs. Holism…Hempel’s
network theory of meaning)
Review- Some possible test
questions
• Hume, Experiments
– What was Hume’s argument? Why do you think philosophers took
it so seriously? Why Was Hume’s argument relevant to science?
Define causation. What role does it play in science? How have
scientists responded to Hume’s problem?
– Why did scientists devise experiments? What are the important
components of experiments? What do experimental methods give
science? Explain how problems like Hume’s led to experiments.
List four ways in which induction can go wrong How do
experiments prevent science from falling into these traps?
– Devise an experiment. Discuss how your experiment is or is not
vulnerable to Hume’s argument. As a scientist, what do you think
you would do about this?
Review, Cont.
• Theories, Comte, Logical Positivists
– Consider the following theory. Explain why it is a good or
bad theory (Hung’s list…) .
– Why was Comte studying the history of science? How did
Comte describe the theoretical stage of science? What was
the connection between Comte and the Logical Positivists?
What is you opinion of Comte’s Theory
– List the three stages that the logical positivists’ definitions
went through.Why did they change? Create a definition for:
Eggs are fragile for each of these. What are some problems
you might run into applying these definitions?
– What were some issues that the Logical Positivists faced?
How did they deal with these issues? Where do the Logical
Positivists stand today?
Current state of philosophy of
science (and science)
• Modern way to define
theoretical terms:
• Provided by the Logical
Positivists
• Still used- e.g.
psychology,
operationalization
• Memory=performance on flash card
test
• Modern method for
doing research:
• How are scientists
doing science these
days?
• Popper!
Karl Popper
1902-1994
Popper wanted to know:
• What is good science?
• How should we decide what is and what is
not science?
To put it another way…
•
•
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•
•
•
•
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When should something be considered ‘scientific’?
Can science find out the truth about everything?
What is the scope of science?
Should science be able to study everything?
Should some topics be excluded from science?
What does it mean if something can’t be studied by
science? If not, why not?
When is an activity scientific?
When is scientific activity ‘good science’? When is it
‘bad science’?
How should science be done?
What should we expect from science?
Some attempts to answer these
questions
• Bacon: Science should use my method. My
method results in good science (because my
method is objective)
• Comte: Science should restrict itself to making
generalizations from observations. Anything
outside of this is outside bad science.
• Logical Positivists: Science can study everything
that is worth studying. Anything that science can’t
define through verification is meaningless.
Popper’s Concerns
• Increasing strangeness of scientific theories
(e.g. quantum physics)
• Dubious credentials of some theories
claiming to be scientific (e.g. Freudian
psychoanalysis, Marxism)
Why did Popper Care?
• Science is supposed to be about the truth
(about objective reality)!
• Bad science is less likely to find the truth.
• Science has a certain status that could be
misused.
Popper’s proposed argument
• All good science is like x (i.e. has the
property x)
• Your theory or story or explanation is not
like x
• --------• Your theory is not good science!
Popper’s Proposed Argument,
more detailed
• All good science follows methodology x
• Your ‘science’ does not follow methodology
x
• -----• Your science is not good science.
Popper and Induction
INDUCTION
The challenge
• Getting rid of induction!
– Aristotle said it could not be done!
– The Medieval Natural Philosophers
couldn’t do it!
– Hume couldn’t do it!
–Can Popper do it?
Popper’s Bright Idea
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Swan x is white
Swan y is white
Swan z is white
----------All swans are white.
It seems fairly easy to determine
the falsity of this statement…
Popper’s Method
• 1. Find a hypothesis (from somewhere, somehow).This
hypothesis must be falsifiable. (Note: theory)
• 2. Using deductive logic, derive an empirical
implication that proves the hypothesis to be false (
like indirect tests)
• 3. Test the implication in some way-to see if it (the
implication, not the hypothesis) is true or false.
• 4. a)If the test shows that the implication is true,
discard the hypothesis and go to 1.
• b) If the test does shows the implication to be false, go
back to step 2.
• Popper called this the hypothetico-deductive method.
Seems like backward science!
•
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Example:
Hypothesis: Apples fall to the ground
If it is false that [apples fall to the ground]
Implication: We should expect to see an apple
hover in the air when released.
• If we carry out the test, the implication is
falsified.
• Therefore we go back to step two and derive
another implication
Some important features of
Popper’s method
• it makes falsification the main activity of
science (black swan detector)
• the more tests a hypothesis passes, the more
corroborated it is.
• science should progress by accumulating
corroborated theories (i.e. hypotheses),
while always being on the lookout for tests
that might falsify these statements.
What counts as science
• All good science follows methodology x
• Your ‘science’ does not follow methodology
x
• -----• Your science is not good science.
• Methodological failure: If there appears to be no
possible test that would prove the statement false,
then that statement cannot be investigated by
science.
Consider the following
statements
•
•
•
•
•
I like bananas or I don’t like bananas.
Apples are a healthy snack.
The acceleration of gravity is 9.8 m/s2.
God is good.
The id controls your subconscious
behaviours.
Metaphysics
• Popper describes theories that cannot be
investigated by science as being metaphysical.
• Popper does not judge metaphysical theories. He
does not, for example, say that they are morally
wrong, or meaningless.
• Popper simply says that metaphysical theories
cannot be evaluated by scientific criteria.
• Some other method of evaluation would need to
be found if they were to be evaluated.
Group Discussion
• If you were in charge of training a group of
new scientists, would you pick Bacon’s
method or Popper’s ( or do something
different)?
• On the board:
– Which would you pick (or what would you
do)?
– One sentence stating why.
Popper and the Logical
Positivists
Different
• Popper is interested in falsification, while the
logical positivists’ theory depends on the idea of
verification
• logical positivism is concerned with meaning.
Popper’s theory does not involve philosophy of
language or the meaning of statements.
• Popper was much less critical of ‘metaphysical
theories’ than logical positivists
Popper and the Logical
Positivists
• The same:
• Popper did think that observational statements
were important, and could provide the basis for
scientific theories.
• Popper wasn’t too concerned with the discovery of
hypotheses. What was important was how
hypotheses were (or were not) justified.
• Both Popper and the Logical Positivists took
Hume seriously.
Problems with Popper?
• 1. Find a hypothesis (from somewhere,
somehow).This hypothesis must be falsifiable.
(Note: theory)
• 2. Using deductive logic, derive an empirical
implication that proves the hypothesis to be false
( like indirect tests)
• 3. Test the implication in some way-to see if it (the
implication, not the hypothesis) is true or false.
• 4. a)If the test shows that the implication is true,
discard the hypothesis and go to 1.
• b) If the test does shows the implication to be
false, go back to step 2.
Two problems
• The infinite loop problem
– “If the test does not show the implication to be
false, go to step 2.”
• The inane hypothesis problem
– “My prof’s name is Jen”
Dealing with the inane
hypothesis problem
• Science should only investigate the truth value of
sentences with high empirical content.
• According to Popper the more likely a statement is
to be false, the higher its empirical content.
• Consider:
• It’s going to rain or be sunny or snow tomorrow
• It’s going to hail for five hours tomorrow.
Empirical Content
• Popper made the intuitive concept of empirical
content more rigorous and quantitative by
introducing the idea of potential falsifiers.
• Potential falsifiers are observation statements that,
if true, makes the statement false.
• The falsifiablity of a statement can be judged by
its number of potential falsifiers.
• The more potential falsifiers a statement has, the
higher its empirical content.
• (parallel with the logical positivists…)
Dealing with the infinite loop
problem
• Hypothesis Corroboration
• Consider hypothesis A:
– Potential Falsifier 1
– Potential Falsifier 2
...
– Potential Falsifier n
• The more potential falsifiers are discarded, the
more the hypothesis itself is corroborated
• Also- more or less severe tests
Trusted Hypotheses
• Eventually, the hypothesis will have passed
so many tests that it will be accepted by the
scientific community.
• They will treat the hypothesis as ‘de facto
true’ and move on to test other hypotheses.
• Even so, scientists must always keep in
mind that it has never been proven to be
true.
Add ons to Poppers Method
• Falsifier: An observation statement, derived
through deductive logic, that can prove a
hypothesis false.
• Empirical Content: Hypotheses with high
empirical content are better than ones without it
• Potential Falsifiers: The more potential falsifiers
a hypothesis has, the higher the empirical content
• Corroboration: Is like truth, but Popper doesn't
want to say it is truth. Depends on the number and
severity of the tests a hypothesis has been through
Compare: Popper’s Method,
Inductive Methods (e.g. Bacon)
• Need to make sure inductive logic is not
hiding in Popper’s method!
• Quick Group Question: Do you think there
is any inductive logic hiding in Popper’s
method?
(I’ll take a poll after the discussion)
Reviewing a few concepts
• Truth and Falsity: Popper’s theory rests on the
idea that they are different.
• Consider:
–
–
–
–
–
–
This chair is orange.
Some chairs are orange.
Some chairs are not orange.
No chairs are orange.
All chairs are not orange.
All chairs are orange.
• How would you prove these true? false?
Reviewing a few concepts
• Induction:
– possibly true conclusions
– way of increasing the truth probability of a
statement is to observe multiple instances that
confirm (but do not prove) the truth of the
statement
– Completely separate from induction is the issue
of indirect testing (auxiliary hypotheses)
Reviewing a few concepts
• Indirect testing:
– Indirect testing involves deriving (deductively valid)
implications of the hypothesis and testing these
implications.
– If the implied statement is true, then we can
(deductively) conclude that the hypothesis is true.
– But the problem of auxiliary hypotheses means that we
can never say for sure that the statement is true- We can
never state all of the premises in our deductive
argument.
Corroboration and Induction
• some similarities between Popper’s scientific
method and the Bacon’s:
• Both employ the idea of deducing observable,
testable consequences from statements.
• In some types of induction (e.g. universal
generalization) multiple observations increase the
probability that a statement is true.
• In Popper’s method, there are multiple tests of
(hypothesis, deduced potential falsifier) pairs
(involving observation of test results.
Key Differences
• Observing the falsity of potential falsifier means
that the hypothesis is not false (deductively).
• Inductively, finding observations consistent with
the truth of the statement suggests that the
statement is true.
• Popper did not want to equate corroboration with
truth. (not false DOES NOT EQUAL is true)
• He intended corroboration as a way to choose
between competing hypotheses, not show that a
hypothesis is true.
• This is a fine line to walk…
Value of Popper
• The idea that non-falsifiable statements
can’t be studied scientifically
• The distinction between truth and falsity
(they are not exactly equivalent)
• A scientific method which at least seems
less reliant on induction... maybe...
• At the very least, a scientific method which
has been generally adopted by science
Review of Popper
• Some sample test questions:
• Define: Empirical Content, Severe Test,
Corroboration. Give examples illustrating these
concepts. What motivated Popper to invent his
method? Was Popper a logical positivist? In what
ways did his theory differ? In what ways was it the
same?
• Pick a hypotheses and create three potential
falsifiers. Which of these is a more severe test?
• Based on what you know of Bacon’s Method, how
might Bacon criticize Popper?
Classic Tradition
• The 1950’s and 1960’s marked the high
point of what is commonly referred to as the
‘classical tradition’ in science.
• What is this ‘classical tradition’?
• It is a certain basic view of the world and of
science which has been shared, to some
extent by all of the philosophers of science
we have considered so far.
Assumptions of the Classical
Tradition
• There is an outside world, which exists
independent from all observers.
• The ultimate goal of science is an accurate (as
possible) description of this observer independent
world.
• Scientists can observe the objective natural world,
in some way, and learn about it.
• the universe has underlying regularities that, if
discovered can explain the behaviour of the
universe.
General Agreement that…
• There is independent observation (if you
had twenty scientists observing something,
they would see it about the same).
• Observation is not dependent on the
particular observer, and deductive logic is
not dependent on the observer.
• Reality is also independent of any particular
observer.
Requirements of Science
• The question is:
• if you lose any of these assumptions, is it still
possible to even do science?
• In other words, can you be a scientist if you don’t
believe in
– An objective reality
– A reality with causal universal laws
– An objective observer (or collectively, a group of
objective observers) who are able to draw objective
conclusions from objective observations of reality.
Two branches of Twentieth
Century Philosophy of Science
• Branch One: Logical Positivists, Popper
• Branch Two: Duhem-Quine Thesis, Kuhn
• Next Class: Talking about Branch Two
• Core ideas: Meaning is subjective,
perception is subjective, science is
subjective.