Basically, Landsburg is positing the existence of a Platonic realm of math that is always "out-there", existing. This is a major map-territory confusion, and should be a warning to rationalists.
I agree; but interestingly, that doesn't imply that mathematical Platonism is false. I'm becoming more and more convinced that the universe is a relatively simple mathematical object, and that this universe existing is a special case of all mathematical objects existing.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).
ETA: It would seem that rationality quotes are no longer desired. After several days this thread stands voted into the negatives. Wolud whoever chose to to downvote this below 0 would care to express their disapproval of the regular quotes tradition more explicitly? Or perhaps they may like to browse around for some alternative posts that they could downvote instead of this one? Or, since we're in the business of quotation, they could "come on if they think they're hard enough!"