# The Joy of Sets

I have a guest post up over at the blog of Oxford University Press, discussing a few amusing tidbits from set theory. The post was inspired by this earlier post, in which I mentioned the bizarre criticism of set theory served up by a publisher of Christian home schooling materials.

In my new post I discuss Russell's paradox, another classic paradox whose name I do not know. and finish with a set-theory-based “proof” that all counting numbers are interesting. (More precisely, I show that the set of boring counting numbers is empty.) Enjoy!

Tags

### More like this

##### Basics: Going Meta
In math and computer science, we have a tendency to talk about "going meta". It's actually a pretty simple idea, which tends to crop up in other places, as well. It's also one of my favorite concepts - the idea of going meta is just plain cool. (Not to mention useful. There's a running joke among…
##### Yummy Delicious Pi
My number theory course has recently moved on to things that are a bit more technical and esoteric than our earlier fare, so I haven't felt they would make good blog fodder. If you need a quick math fix (and who doesn't?), you can have a look at this guest post I wrote for the Oxford University…
##### Set Theory, Now?
During my time in New York, I had lunch with some friends from England. We were discussing evolution and creationism, and religious fundamentalism more generally. Somewhere along the line I mentioned that creationists routinely use mathematical arguments in their writing, and one of my friends…
##### Why Axiomatize Set Theory?
Naive set theory is fun, and as we saw with Cantor's diagonalization, it can produce some incredibly beautiful results. But as we've seen before, in the simple world of naive set theory, it's easy to run into trouble, in the form of Russell's paradox and a variety of related problems. For the…

The one whose name you don't know is the Berry paradox (first discussed in print by Russell, I believe).

By Glenn Branch (not verified) on 13 Sep 2012 #permalink

Fallacies of self-reference...that's why it's never polite to talk about oneself.

Type theory and the Lambda calculus were created to solve this problem. As Godel said, set theory and the theory of types "permits the derivation of modern mathematics and at the same time avoid all known paradoxes."

Fun with fuzzy definitions!
Here are some more, see if you can spot the paradoxes just waiting to be assigned someone's name. Claim yours today!
Sa == The set of all ideas too abstract to be included as an element of a set without resulting in either that set or its complement leading to a self-referential paradox.
Ra == The set of all ideas just abstract enough that every living person except Bertrand Russell considers them insufficiently precise to be enumerated as a member of a set.
Ca == The set of animal shapes visible in the clouds in the sky.
~Ca = The complement of that set.

Small criticism: Writing for a general audience like this (or probably for any audience, but more crucially for a general audience), I think it's advisable to analogize Russell's paradox to "the barber who shaves every man in town who doesn't shave himself". Speaking solely for myself, when I first read Russell's paradox, I was like, "Wait, wut?", and then read the barber example, and I immediately understood both. I would have gotten Russell's paradox eventually, but the barber thing made it a lot easier to latch onto.

By James Sweet (not verified) on 16 Sep 2012 #permalink

I apologize if commenting was intentionally closed on the last post, but I am unable to add to it. I wish to comment that, even as a non-materialist, I do not see the issue with using the word "crisis" in the context of evolutionary theory. The word is used in mathematics, but it does not make people doubt whether they have received the right change.

The question should be: is evolutionary theory sufficiently strong that like math it has ineluctably become part of general knowledge, regardless of current academic developments? An anecdotal answer would be that, while it is possible to become, say, a successful rocket scientist without subscribing to evolutionary theory, the same is not true of mathematics.