How to introduce advanced set-theoretical objects to philosophy students?
First, I apologize if MSE is a bad fit for this question. I'm going to give a course as the last course of "elementary set theory" (the previous courses were not given by me). I planed to introduce some advanced topics like the constructible model, the axiom of determinacy and forcing, but not limited to them. The problem is the listeners are philosophy students. They got very little mathematical training. I can not introduce them in a very formal way.
But I still want to impress them by explaining my ideas more intuitively and philosophically. In particular, what's the philosophical meaning behind set-theoretical objects? Are there some theorems, related to mathematical logic, that the philosophy students may have interest?
Solution 1:
i) I would check out Michael Potter's wonderful Set theory and Its Philosophy to see the kind of thing that it might be sensible to cover in a course directed to not-very-mathematical philosophers. This brilliant book was written for, inter alia, just such students.
ii) You can introduce the constructible model and talk a little about $V = L$ without losing your audience. But I very, very, much doubt that, if your audience is philosophers with little mathematical background, that there is any point at all in trying to explain forcing. Even Timothy Chow's Beginner's Guide will be beyond them (and coming up with anything more accessible is an unsolved exposition problem). What will matter to your audience, as far as reflection on set theory is concerned, is that certain independence results can be proved, not any of the details of how they are proved.
iii) I would recommend, given your audience, and given they have had a standard intro to ZFC, spending some of your time looking sideways rather than upwards. They need to know (and will be really interested in discovering) that there are other ways of doing set theory: not just Scott-Potter (which arguably fits more nicely the canonical hierarchical picture of the set universe), but say NF.
Solution 2:
Here are a few additional resources that may be of interest:
An older but very interesting book, Foundations of set theory by Abraham Fraenkel, Yehoshua Bar-Hillel, and Azriel Lévy. The book describes the axioms for ZFC but is particularly interested in their motivation and with other philosophical issues in set theory.
The paper "Does mathematics need new axioms?", Solomon Feferman, Harvey Friedman, Penelope Maddy and John Steel, Bulletin of Symbolic Logic, 2000. Concerns issues such as whether large cardinal hypothesis should become part of the standard framework for mathematics.
A very recent philosphical paper by Joel David Hamkins, "The set-theoretic multiverse", Review of Symbolic Logic, 2012. Hamkins explicitly focuses on the philosophical problem of the objective meaning (or lack thereof) of the phrase "all sets". I think that philosophy students may be able to get something out of this paper if they have been introduced to the continuum hypothesis and L, even if they known nothing of forcing. And it is extremely timely.
Solution 3:
If your students are still having difficulties with more basic concepts of formal proof, may I humbly suggest my DC Proof program as at least a supplementary resource. The tutorial included with my easy-to-learn proof assistant includes worked examples of, among other proofs, a resolution of the Barber Paradox, its set-theoretic twin, Russell's Paradox, and the related paradox of the universal set -- enough to pique the interest of any philosopher! I also introduce the axioms for the natural numbers and prove by induction that no number can be its own successor. With each of 13 worked examples, I include exercises with hints and full solutions.
Visit my website for more information, a free download and demo video/PowerPoint slides.