Will_Sawin comments on Rationality Quotes: January 2011 - Less Wrong

2 Post author: wedrifid 03 January 2011 05:24AM

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Comment author: Will_Sawin 04 February 2011 06:22:00PM 1 point [-]

What's specifically going on here is that (P=>Q) => (Q=> P) is false whenever P is false and Q is true.

Adding it as an axiom schema to propositional calculus results in a contradiction. It cannot be added as a single axiom to first-order logic.

Comment author: JoshuaZ 04 February 2011 10:18:45PM 0 points [-]

Yes, you are correct. I was confused in a very stupid way.