I would like to comment on Vaughan Pratt's Phew, thanks Richard, no fun defending a position alone. Here's another argument for Choice, no more or less a proof than the clarity-of-mathematical-thought argument, it seems to me. "Proof" of AC. It took mathematics about thirty years longer to imagine AC false than it did to imagine it true. This "argument" can be applied in other situations. Applying it to Grothendieck universes (aka inaccessible cardinals) would suggest that they don't exist. We can imagine their nonexistence (their existence is independent of ZFC) but so far we haven't been able to imagine their existence (a proof in ZFC that they don't exist is still on the cards). What arguments exist in *support* of the existence of Grothendieck universes? I see the "cogito ergo sum" argument, what else? Vaughan Pratt