shminux comments on [SEQ RERUN] Math is Subjunctively Objective - Less Wrong

2 Post author: MinibearRex 12 July 2012 02:07AM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Comments (15)

You are viewing a single comment's thread. Show more comments above.

Comment author: shminux 12 July 2012 05:51:28AM 1 point [-]

What he is really asking is "why do we think that Peano arithmetic is true?".

Comment author: dbaupp 12 July 2012 10:11:51AM *  1 point [-]

I've never quite grokked this, is "true" an abbrevation for "true in this universe"? Because asking if a mathematical theory is "true" otherwise is just wrong.

(ETA: Any reason for the downvotes? This is a genuine question.)

Comment author: Nick_Tarleton 12 July 2012 07:54:51PM *  1 point [-]

It seems to me that he's talking at least as much about the fact that S(S(0))+S(S(S(0)))=S(S(S(S(S(0))))) is a theorem of PA, and asking what it means for that to be "true".

Comment author: Decius 16 July 2012 05:47:05PM 0 points [-]

Peano arithmetic does not have a truth value. Peano arithmetic provides the definition of 2,3,5,+,and =.

In other words, if you don't accept Peano arithmetic, then you cannot decode what I mean by 2+3=5

Comment author: shminux 16 July 2012 05:54:55PM 1 point [-]

Peano arithmetic does not have a truth value.

Depends on your definition of true:

Because two sheep plus three sheep equals five sheep, and this appears to be true in every mountain and every island, every swamp and every plain and every forest.

This statement is clearly not about accepting PA, but about counting sheep.