[FOM] Falsify Platonism?
Timothy Y. Chow
tchow at alum.mit.edu
Wed Apr 28 14:41:11 EDT 2010
Daniel Mehkeri wrote:
> For the record, I thought a platonist was more or less someone who, say,
> has a non-trivial opinion about the continuum hypothesis. I can accept
> the distinction between "set-theoretic" and "number-theoretic"
> platonism, as Bill Taylor called it, but even the latter means something
> stronger than finitism.
I could perhaps be swayed here, because we're starting to split hairs
about what the word "platonism" means. However, I still think that
there's a distinction between being a platonist about the natural numbers
and being a platonist about first-order logic. Later on you wrote:
> Set theory wasn't the foundation of anything a century ago. It is
> now, though not necessarily so, and many are not really platonists
> about them anyway.
>
> The natural numbers have always been fundamental and always will be.
The natural numbers, sure, but first-order logic hasn't been foundational
for nearly that long. We're not about to give up on the natural numbers,
but I think there's more room for giving up on the claim that every
first-order formula of arithmetic expresses a meaningful property of the
natural numbers. That's why I still see a distinction.
> Mahlo cardinals are very old, and are often alleged to follow from the
> iterative concept of set plus the idea that we shouldn't be
> unnecessarily restrictive about what counts as a set. I think platonists
> are really quite confident about these, so this would be fairly
> profound.
Could be. I'd be curious to poll set theorists on this one. Maybe it's
not until measurable cardinals that some acrophobia starts to set in.
Tim
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