Larks comments on Second-Order Logic: The Controversy - Less Wrong

24 Post author: Eliezer_Yudkowsky 04 January 2013 07:51PM

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Comment author: Qiaochu_Yuan 04 January 2013 11:09:38PM 5 points [-]

I think the point of the fable is that Yesenin-Volpin was counting to each number in his head before declaring whether it was 'real' or not, so if you asked him whether 2^50 was 'real' he'd just be quiet for a really really long time.

Comment author: [deleted] 04 January 2013 11:13:30PM *  3 points [-]

But wouldn't that disprove ultrafinitism? All finite numbers, even 3^^^3, can be counted to (in the absence of any time limit, such as a lifespan), there's just no human who really wants to.

Comment author: Larks 04 January 2013 11:19:59PM 5 points [-]

Well, that's what the anti-ultrafinitists say. It is precisely the contention of the ultrafinitists that you couldn't "count to 3^^^3", whatever that might mean.

Comment author: SecondWind 05 January 2013 02:55:47AM 0 points [-]

Hmm.

So, it's not sufficient to define a set of steps that determine a number... it must be possible to execute them? That's a rather pragmatic approach. Albeit it one you'd have to keep updating if our power to compute and comprehend lengthier series of steps grows faster than you predict.

Comment author: Larks 05 January 2013 02:01:54PM 0 points [-]

No, ultrafinitism is not a doctrine about our practical counting capacities. Ultrafinitism holds that you may not have actually denoted a number by '3^^^3', because there is no such number.

Comment author: Peterdjones 05 January 2013 02:13:34PM 3 points [-]

Utlrafrinitists tend no to specfify the highest number, to prevent people adding one to it.

Comment author: Larks 05 January 2013 09:31:31PM 2 points [-]

Hence "may not"