Re: JQ Test 1.0

From: Chris Capel (
Date: Tue Jan 31 2006 - 13:06:55 MST

On 1/30/06, Eliezer S. Yudkowsky <> wrote:
> Philip Goetz wrote:
> > On 1/28/06, Eliezer S. Yudkowsky <> wrote:
> >
> >>The way to explain logical "if" to humans is to rephrase "P => Q" as "~P
> >>or Q" which is mathematically equivalent and makes much more human sense
> >
> > The problem is that the word "implies", as we use it in real life,
> > cannot be reduced into a Boolean truth table. The difficulty people
> > have in understanding Boolean "implies" shows the poverty of Boolean
> > logic, not the poverty of human reasoning.
> It shows that you have to do some extra work to translate Boolean logic
> into English. Humans, when we hear "if...then", tend to hear evidential
> implication or counterfactual implication, not material implication;
> these are all distinct structures. And, yes, only material implication
> has a Boolean truth table, but that doesn't make it useless.

> To use the connective of material implication in human discourse, one
> should, I suggest, say "~P or Q". If/then has a quite different meaning
> in English. We do not say, "If the moon is made of green cheese, then I
> have four arms" or "If birds fly, then I have two arms" or "If I have
> four arms, then I have two arms". By contrast, "I do not have four
> arms, and/or I have two arms" makes perfect sense in English.

Interestingly, (if I have all this straight,) there are a few
idiomatic English phrases using "if" in which the correct
interpretation is material implication. The one I just noticed is "I'm
damned if I'll do that."

But, of course, you're right in general. That meaning is specific to
those idioms.

Chris Capel

"What is it like to be a bat? What is it like to bat a bee? What is it
like to be a bee being batted? What is it like to be a batted bee?"
-- The Mind's I (Hofstadter, Dennet)

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