prase comments on Algorithms as Case Studies in Rationality - Less Wrong

27 Post author: abramdemski 14 February 2011 06:27PM

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Comment author: prase 15 February 2011 06:07:32PM *  2 points [-]

"does that imply that?"

Because in casual speech the question doesn't actually mean "does that imply that?", but rather "do we have a derivation of that from that, using our set of inference rules?" Not the same, but people seldom realise the distinction.

Comment author: Johnicholas 15 February 2011 09:29:39PM 4 points [-]

This is the "paradox of the material conditional", which is one of the primary motivations of relevance logic - to provide a sentential connective that corresponds to how we actually use "implies", as opposed to the material (truth-functional) implication.

http://plato.stanford.edu/entries/logic-relevance/

Comment author: abramdemski 16 February 2011 12:34:11AM 0 points [-]

Good point! Perhaps you won't be surprised, though, if I say that my own preferred account of the conditional is the probabilistic conditional.

Comment author: abramdemski 15 February 2011 07:47:00PM 0 points [-]

That is also a fair interpretation, especially for those students who just want to get the homework done with and don't really care about increasing their sureness in the theorem being re-proved.

If we additionally care about the argument and agree with all the inference rules, then I think there is a little more explaining to do.

Comment author: prase 16 February 2011 10:15:19AM 0 points [-]

Not only for the students, I think. Confusion between implication and inference was enough widespread to motivate Lewis Carroll to write an essay, and nothing much changed has since then. I didn't properly understand the distinction even after finishing university.