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…

• 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 I (will) take my umbrella

If it is raining then I (will) take my umbrella

True True ?

True False ?

False True ?

False False ?

Lets check our intuitions with a poll…(first, write down what you think)

Owls eat mice

Ice Freezes If Owls eat mice then ice freezes

True True ?

True False ?

False True ?

False False ?

More intuition checking…

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

Statement A Statement B If Statement A then Statement B

True True True

True False False

False True True

False False True

The logicians must make a decision…(Studies in Logic,. Charles Pierce, 1883,Tractatus Logico-Philosophicus- Wittgenstein, 1921)

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 Popper1902-1994

Popper wanted to know:• What is good science?• How should we decide what is and what is

not science?

To put it another way…• 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

• 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!

• 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.