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From: wex@milano.UUCP
Newsgroups: sci.philosophy.tech
Subject: Re: Uncertainty in life
Message-ID: <4603@milano.UUCP>
Date: Tue, 26-May-87 18:27:56 EDT
Article-I.D.: milano.4603
Posted: Tue May 26 18:27:56 1987
Date-Received: Thu, 28-May-87 00:56:27 EDT
References: <6762@mimsy.UUCP> <13261@watmath.UUCP> <3978@sdcc3.ucsd.EDU>
Sender: wex@milano.UUCP
Organization: MCC, Austin, TX
Lines: 30
Keywords: Heisenberg certain Descartes
Summary: Certainty and ~X

In article <13261@watmath.UUCP> erhoogerbeet@watmath.UUCP (Edwin (Deepthot)) writes:
> Let us assume that there is nothing that can be known for certain. Then,
> a contradiction is reached because we have taken as certain the hypothesis
> that nothing can be known for certain. Therefore, it must be so that you can
> know something for certain.

Readers of talk.philosophy.misc have argued this on out months ago.  The
fallacy lies not in knowledge (as Steve assumes below) but in a linguistic
trick.  Try the following formulation:
	"I am reasonably sure (P > .999999) that nothing can be known
	 for certain."
This claim does not itself contain a claim of certainty, merely an assertion
of probability.  Thus, no contradiction.

In article <3978@sdcc3.ucsd.EDU>, ma188saa@sdcc3.ucsd.EDU (Steve Bloch) writes:
> If X cannot be proven, then ~X cannot be disproven...

I can see I'm going to have to dig out my archives on intuitionist logic.
Steve's statement is problematic only in two valued logic.  There are logics
in which X can be any of {True, False, Unproven}.  Thus, I can show that X
is not false and not have shown that it is true.  More formally, in a
three-valued logic, ~(~P) ==> P is no longer the case.


-- 
Alan Wexelblat
ARPA: WEX@MCC.COM
UUCP: {seismo, harvard, gatech, pyramid, &c.}!sally!im4u!milano!wex

Shit happens.