Philosophy of Science 80-220

Current News:

Hi everyone.  Thank you for being well prepared and having a lively class discussion.

I have added some reading assignments for the second part of the course on confirmation.  The readings will be in a handout, so if you miss class on Wed. you will have to get it from my mailbox (next to my office door at 135K Baker Hall).

Syllabus

Basic Information:

Instructor: Kevin T. Kelly.

• E-mail: kk3n@andrew.cmu.edu.
• Phone: X8567.
• Office: 135 BH.
• Office hours: Monday 1:00-2:00, Wed: 2:00-3:00, or by appointment.

• Thomas S. Kuhn, The Copernican Revolution
• David Papineau, The Philosophy of Science

Description:

What is an explanation?  What is a cause?  What is confirmation?  What is probability? What justifies drawing conclusions beyond the data?  How does logic differ from science?  Does science aim at truth? Explanation? Prediction?  Do scientific terms denote objects or do they merely serve as calculational devices?  Is there a scientific method?  Is there a role for subjectivity?  Are there any objective rules in science at all?  Is science just politics?  Is there such a thing as objective evidence in scientific debates?

Reasonable (and famous) people have differed sharply as to their answers.  We will survey some answers proposed to some of these questions.  This is not a closed subject.  You may come up with a better idea!

The material is not dogmatic or generally conceded, so it lends itself to discussion.  In order to get you thinking, I will put issues on the table in a loose lecture format.  Also, I will give some lectures on some of the logical and probabilistic ideas as they arise.

Level of the Course:

Although the course material is not so difficult, it demands a certain intellectual maturity to keep a clear grasp on the point at hand.  At the end of the day, you will not be told what the "right" answer is.  You will have to master several conflicting positions and not confuse them.  You will have to understand and construct arguments instead of calculating the answers to exercises.  All of this is typical of any subject, including science, at the advanced graduate level, but most people encounter it first in undergraduate philosophy classes.

Aims of the Course:

It is not an aim of the course to march through a fixed range of material.  The textbook is a loose collection of articles and the schedule gives us little time to explore each topic in depth.  If there is support for the idea, we can extend a topic (e.g., confirmation).

General Requirements

This is a discussion course.  I expect enthusiastic and well-informed class discussion.

Discussion groups:

I may ask you to break into discussion groups and report your findings.

Attendance:

Reading assignments are due in class.

Punctuality:

A 10% per day late penalty applies to all written assignments. Days are measured from the end of class.
To account for health and family contingencies, your lowest two reading assignments will be dropped from your average.

Reading Assignments:

The philosophical material is tricky.  It's kind of like stage magic: by the time you even start to wonder how the lady will get out of the box, she is already smoking backstage.

Whenever you read a philosophical article, have a notebook at hand and follow this procedure:

1. Find the author's conclusion.  Write it as simply and crisply as you can.
2. Reconstruct the author's argument for the conclusion, noting all the basic assumptions.  Be very concrete about this.  List the assumptions, and then derive the conclusion from them by logical reasoning.
3. If the conclusion doesn't seem to follow, think of assumptions that would make it follow.
4. Some assumptions may be left unstated because they are obvious or the author doesn't want to call attention to them
5. Think about whether you agree with the assumptions.  Try to think of cases in which they would be false.
6. In the end, you should have

I may call on you to state an author's argument from your notes in class.

Written Assignments and Grading

Simple reading questions are published with each reading assignment on the web.  These exercises give you some official credit for being prepared for class discussion.

They are due in class on the date indicated.

Answers must be typed.

Keep the answers as short and crisp as possible.  I expect no more than a couple of sentences per question.  Try to say something that convinces me you read the text instead of guessing.

Your two lowest scores will be dropped from the average to account for broken computers, illness, etc.

Midterm Paper Assignment (33% of the grade)

Length:  5 pages plus references.

Essay must be typed, double spaced, 10 pt. Times Roman, with proper references.  See paper writing guide.

Option 1:  Philosophical theories of scientific justification are often judged by their ability to make sense of the history of science.  Analyze the Copernican Revolution (or some other scientific episode you know about)  from the point of view of one or more of the approaches to confirmation and induction discussed in the course.  Argue either that the philosophical theory does a good job of accounting for the case or that it fails to make sense of important aspects of the case.

Option 2:  Bayesianism is a very flexible approach.  Try to show that some of the other confirmation theories we have looked at can be understood to be applications of Bayesian principles.

Option 3:  Discuss the relative merits of Naturalism and of its alternatives.

Option 4:  Write an expository essay on any other topic that pertains to more than one of the confirmation readings.  Give me a written proposal with references first.

Final Paper Proposal (counts as one reading exercise)

Due Nov 21.  Start doing library work by Nov. 12.

One page outline of your final paper, with a list of plausible references included.

Final Paper Assignment (34% of the grade)

Due last day of class (Dec 11).   Get started as soon as your prospectus is approved.

Essay must be typed, double spaced, 10 pt. Times Roman, with proper references. See paper writing guide.

seven pages + footnotes and bibliography.

Option 1:  Argue for or against scientific realism, illustrating your position with indendent research in the history or present practice of some science.  Try to keep it crisp and stick to arguments rather than opinion.

Option 2:  Analyze the rationality of a historical scientific development in terms of one or more of the theories of confirmation discussed in class.  Check the linked list of scientific episodes.

Option 3:  If there is no logic of discovery, what are A.I. people doing when the write computer programs for learning from experience?  Compare the articles on discovery in the text with some of the machine learning literature (e.g., Herb Simon's BACON program).  I can help with references.

Option 4:  Compare two of the accounts of explanation discussed in class in light of real scientific examples drawn from library research.

Option 5:  Any other critical topic that interests you and that brings outside scientific reading to bear on more than one of the articles examined in class.  Consult me early (by April 5) for guidance on this option.

You will be graded first on competent description, second on cogent argumentation, and third on originality.

I. The Copernican Revolution

For those of you who looked at  the case with me in 80-120, you will find that Kuhn's presentation expands upon Cohen's.

Some related links:

• Internet Modern History Sourcebook: The Scientific Revolution
• Online Encyclopedia Britannica: The Scientific Revolution.
• Biographical search engine for the scientific revolution

Aug 29:  The Two-Sphere Universe.  Kuhn Chap 1 and Technical Appendix section 1:

1. Define north, the solstices, and the equinoxes in terms of gnomon observations.  Draw a picture illustrating the definitions.
2. How are north, the solstices and the equinoxes defined theoretically in terms of the two-sphere model?
3. What were the ancient plausibility arguments for the two-sphere model?
4. What phenomena are logically systematized by the two-sphere model?  How does Kunn distinguish explanation from usefulness for prediction?   (Wake up when words like "explanation" are discussed!)
5. Why were the more "modern" views of Leucippus, Pontus, and Aristarchus ridiculed and rejected?  (Give both reasons and remember them.  They will be important when we get to confirmation theory).

Sept. 5:  The Problem of the Planets and Aristotle. Kuhn Chaps 2, 3:

1. By what observable property were the planetary orbits ordered?  Which planets were left unordered by this principle?
2. What problem posed by Plato did Eudoxus attempt to solve?
3. What obvious phenomenon did epicycles account for that Eudoxus' theory did not?
4. Define "equant", "eccentric", and "major" and "minor epicycle".  Why didn't Copernicus like equants?
5. Was Ptolemy's theory ever refuted by the data?  What was wrong with it?  (This is a very important question).

1. How did later astronomers try to fit epicycles into Aristotelian physics?  How did this lead to spurious measurements of the diameter of the universe?
2. Distinguish Aristotle's sublunary physics from his celestial physics.
3. Why would admission of infinite space or a vacuum undermine Aristotle's physics?
4. How did Aristotelian physics foster astrology and how did astrology undermine Aristotle's physics?
5. What two advantages did Aristotle's theory have over those of his contemporaries?

• My Introduction to Aristotle's Physics.
• Aristotle's works (See for yourself, especially, the Physics.)
• Zeno's paradoxes (See Zeno prove the mystical thesis that motion is impossible. That makes short work of physics).

---

Sept. 12:  Medieval Developments.  Kuhn, Chap 4.

1. When did Western Europe lose the Greek texts and when did it recover them?
2. Contrast Hellenic and Hellenistic astronomy.
3. What was Aquinas' achievement?
4. What was the moral significance of the Aristotelian cosmos in the 14^th c.?
5. What did Oresme do?
6. How did Buridan's impetus theory differ from Aristotle?s account of projectile motion?
7. Contrast the assimilation of Ptolemy with that of Aristotle.
8. What practical concerns heightened the importance of astronomy in the Renaissance?
9. Contrast the texts recovered in the 15^th c. with those recovered in the 12^th c.
10. How did new translations of Proclus affect Renaissance science?

Sept 17:  Copernicanism.  Kuhn, Chap 5.

Reading Questions:

1. Why did Copernicus find the current Ptolemaic system to be monstrous?
2. What does Copernicus himself cite as the main advantage of heliocentrism?
3. Why is it so important to Copernicus that the ocean and atmosphere make Earth into a perfect sphere?
4. How does Copernicus reply to Aristotle's argument from natural motion to the fixity of the Earth?
5. How does Copernicus' account of gravity differ from Aristotle's? (Where did he get it from?)
6. Describe Copernicus' explanation of retrograde motion. Provide a picture.
7. Describe Copernicus' explanation of the seasons. Provide a picture.
8. What is the problem of stellar parallax?
9. How did Copernicus objectively order the orbits of the planets?
10. Was Copernicus' system more accurate or simpler than Ptolemy's?

1. My notes on the Copernican Revolution.
2. Copernicus' Preface to De Revolutionibus .
3. Nikolaus Copernicus On the Revolutions of Heavenly Spheres. Charles G. Wallis (Translator).
4. Photographs of De Revolutionibus.

Sept. 19:  Reception.  Kuhn, Chap. 6.

Reading questions:

1. What was the significance of the Prutenic tables for the reception of Copernicus' work by astronomers?
2. Contrast Copernicus' early reception by astronomers and non-astronomers.
3. Did Copernicanism initially fare better among Catholics or Protestants, and why?
4. What accounts for the changing Catholic attitude toward attacks on the Aristotelian cosmos in the early 17th c.
5. During which period did the tide turn in favor of Copernicanism?
6. What was the Tychonic system and what were its advantages?
7. Why were Tycho's parallax measurements on comets and novas so important?
8. State Kepler's three laws of planetary motion.  Where did the first law come from?
9. Why was it so important that stars seem to shrink when viewed through a telescope?
10. What other telescopic observations supported Copernicanism?

II. Induction and Confirmation

Sept. 24:  Carl Hempel: Studies in the Logic of Confirmation

This paper shaped a whole approach to the philosophy of science.  Don't be put off by all the technical-sounding stuff.  The motivation and principles he discusses along the way have been very influential in the philosophy of science, so it is worth looking at.  Stay awake and look for presuppositions you might challenge.  The reading questions will help you to focus on some relevant points.  They will be more critical in character than before.

I took a course with Hempel in 1981 and drove him to the airport when he left Pittsburgh for Princeton after his retirement.  He was a very congenial gentleman and an animated lecturer.

Some reading  notes:

1. Carl Hempel was a close associate of the logical positivist's "Vienna Circle".  The basic idea of the logical positivist movement was to use logic as a tool to model scientific method the way it had already been used to analyze the foundations of mathematics by Gottlob Frege and Bertrand Russell.  Thus, Hempel expects applause when he repeatedly draws an analogy between scientific confirmation on the on the one hand and logical proof on the other.  That is also his excuse for gratuitous technicality throughout the paper.
2. When Hempel says "A entails B" he means "if A then B".
3. "(x)(Red(x))" abbreviates "for all x, x is red".
4. "(Ex)(Red(x))" abbreviates "there exists an x such that x is red".
5. "All ravens are black" is translated into logic as "(x)(Raven(x) ---> Black(x))", or "for all x, if x is a raven then x is black".
6. Read footnote 24.
7. Hempel's proposed theory is a mess so I cut it from your reading.
8. Footnote 27 pertains to question 7 below.

1. What does Hempel want to provide a theory of?
2. What is "inductivism" and how does Hempel criticize it?  Do you agree?
3. Why does Hempel think problem (A) is prior to problem (B)?  Can you think of an objection to that conclusion?  Try to think of an analogous concept where the qualitative version is slippery but the comparative concept is not.
4. Hempel considers whether his project rests on which false assumption?  How does he respond?
5. What is Nicod's criterion of confirmation and what are Hempel's two objections?
6. What are the "paradoxes of confirmation"? (These are famous).
7. What is Hempel's solution to the paradoxes?  Do you agree?
8. State the "special consequence condition".  Does Ptolemy's theory provide an intuitive counterexample?
9. Why can't you adopt the special consequence condition, the converse consequence condition, and the entailment condition all at once?  Give the argument.
10. What is "material adequacy"?

Sept. 26:  Two articles by Rudolf Carnap:

1. Statistical and Inductive Probability

2. On Inductive Logic.

deductive logic is to complete support as logical probability is to incomplete support.

Carnap was a leader in the positivist's Vienna Circle, developing many of its main ideas.  He felt that the new mathematical logic of Frege and Russell gave him an advantage over earlier advocates of degrees of empirical support like Laplace and Keynes. He actually picked up the idea of logical probability from a pre-mystical Wittgenstein, during the latter's tumultuous visit to the Vienna Circle.

Reading hints:

You shouldn't have much trouble with the first article.  The article "On Inductive Logic", is needlessly difficult to understand.  The concepts are actually quite simple, so I'll explain them myself. My hints should more or less save you the work of  reading the article up to section 9.  If you aren't used to mathematical definitions, don't panic.  The terms introduced below mean nothing more or less than what the definitions say, so no background is required.

Reading hints.

Reading Questions on first article:

1. How do inductive probabilities differ from statistical probabilities (e.g., what are they attached to)?
2. What is the principle of indifference and how did Reichenbach and Von Mises object?  How does Carnap object?
3. What are prior probabilities and what are methods I and II for assigning them?
4. How does Carnap propose to avoid the paradoxes of indifference?
5. Why does Carnap choose method II over method I?

1. To make sure you get the idea:  list all the isomorphism classes of state descriptions for the language with two predicates P(_), Q(_), and two individuals a, b (easiest on a word-processor:  cut and paste a lot and add - signs where required).  Next to each state description, write the value of m* for that state description.  Use the table to calculate c*(P(a), Q(b)).
2. What is a direct inference?
3. What is an inverse inference?
4. What "astonishing" consequence does Carnap's theory have for the confirmation of universal laws?  How does he try to address this consequence?  What do you think about that?
5. What kind of "justification" of induction does Carnap approve of?

Oct. 1:

Goodman: The New Riddle of  Induction and

Savage: Implications of Personal Probability

After Goodman's article, philosophers of science lowered their ambitions from finding an objective logic of empirical support to merely identifying some "rational" constraints on changes in admittedly subjective degrees of belief.

The view that probabilities on hypotheses are just somebody or other's willingness to bet on the proposition is now called Bayesian methodology, after the Reverend Thomas Bayes.  The idea that there is no justification for belief but, nonetheless, we are psychologically wired to become more confident in light of increasing evidence goes back at least to David Hume in the 18th century.  The view was revived in this century by the philosopher/mathematician Frank Ramsey.  J. M. Keynes, the famous economist who first proposed the logical interpretation of probability pursued by Carnap, was completely converted to the Bayesian or "personalist" position by Ramsey.

L. J. Savage, a Bayesian statistician, was a major figure in laying the foundations of Bayesian statistics, the official view of the Carnegie Mellon statistics department.

I have included some notes on Bayesian methodology that complement Savage's more foundational discussion.  Please study them. They contain ideas that may be useful for your midterm paper.

Reading Questions:

1. Why is it important to distinguish lawlike from accidental statements?  How does this point relate to Carnap's theory?
2. What is the point of the blue/green vs. grue/bleen example?
3. What is the starting point for the theory of personal probability?
4. What is an example of an objective, normative constraint on personal degrees of belief?
5. What is Savage's model of the objectivity of scientific knowledge?
6. What is the "paradox" of the objectivity of classical statistics?
7. What is Savage's view of logical or "necessary" theories of probability like Carnap's?
8. How does Savage respond to the objection that a theory of gambling preferences is too mundane to serve as a foundation for science?
9. How does Savage respond to Carnap's view that there are two kinds of probability?
10. Why does personalism leave one with no foundation for one's current beliefs?

Oct. 3:

Gilbert Harman:  The Inference to the Best Explanation.

Clark Glymour:  Relevant Evidence

Clark Glymour is a professor in our philosophy department.  So if you have any complaints about his theory, go tell him! This article was very influential.  Unlike the preceding papers, Glymour's emphasizes the importance for confirmation of "unification" or "harmony" of the sort we saw in Copernicus' theory.  For this reason, Glymour's theory has lots of applications in real science and my be of use to you in composing your midterm paper.  Glymour claimed that his theory is not Bayesian.  But a Bayesian, Roger Rosencranz, claimed that Glymour's ideas follow from Bayesianism.  While you ponder this, go back and look at my notes on Bayesianism, under the heading of "unification".

The idea is simpler than Glymour makes it sound.  His idea is just that the hypotheses that are confirmed in a theory are the ones that can be "cross-checked" by using the data and other hypotheses in the theory to compute values for their theoretical quantities in different ways that might possibly agree.  So for example, the observation of two planets tests Kepler's third law relative to the assumptions of Copernican astronomy, but the observation of one planet does not, since Kepler's law relates the radii and velocities of different planets.  If the data could not have turned out in such a way that the hypothesis is refuted given the rest of the theory (i.e., if the hypothesis is not "at risk" from the data, given the rest of the theory), then even if the theory is consistent with the data, the hypothesis is not confirmed by the data.  Even though two theories make the same predictions with equal accuracy, the hypotheses in one theory may be cross-checked against one another better than the hypotheses of its opponent.

That sounds good, doesn't it?  Here's a question for you to ponder.  If both theories make exactly the same predictions, how could relying on "internal cross checking" possibly allow you to determine which is true unless God told you in advance that he would produce phenomena in a unified or internally cross-checkable way?

If you find the article rough sledding, make sure to look at the quote of Weyl on p. 334, which presents the idea very simply.  Don't worry about the details of the generalization to logical theories under heading III.

There is typo on p. 333:  the equation should be

X(f₁(E₁ ... E_k), ...,  f_i(E₁ ... E_k)) = 0.

1. What is "enumerative" induction and how does Harman argue that hypothetico-deductivism is more fundamental?
2. What feature of knowledge does the hypothetico-deductive approach explain that enumerative induction cannot explain?  It could have been said more clearly.
3. Why does Glymour think the hypothetico-deductive account failed?
4. What is Glymour's objection to subjective Bayesianism?
5. How do scientists compute values of theoretical quantities?  Use your knowledge of Copernicus' determination of the diameters of the superior planets to illustrate this point.
6. Why is hypothesis (1) not confirmed by an observed value of A₁?
7. Why is variety of evidence good, and how does Glymour define "variety" with respect to a theory?
8. How does Thirring's theory illustrate the point that accurate prediction does not suffice for confirmation?
9. How does Glymour characterize theoretical simplicity and what does it have to do with confirmation?
10. What is holism?  What part of holism does Glymour agree withand what part does he disagree with.