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From: ladkin@kestrel.ARPA (Peter Ladkin)
Newsgroups: net.math,net.philosophy
Subject: Re: Tarski's definition of truth
Message-ID: <5961@kestrel.ARPA>
Date: Tue, 18-Mar-86 21:39:35 EST
Article-I.D.: kestrel.5961
Posted: Tue Mar 18 21:39:35 1986
Date-Received: Fri, 21-Mar-86 04:49:32 EST
References: <12411@ucbvax.BERKELEY.EDU> <12454@ucbvax.BERKELEY.EDU>
Organization: Kestrel Institute, Palo Alto, CA
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Xref: watmath net.math:2984 net.philosophy:4537

In article <12454@ucbvax.BERKELEY.EDU>, weemba@brahms.BERKELEY.EDU 
(Matthew P. Wiener) writes [regarding Tarski's truth defn]:
> Two points.  First truth in logic refers to truth in some model.
> Not to any absolute truth.  Second, any logical sentence can be
> broken down into well determined atomic formulas.  Each of these
> atomic formulas has a definite truth value within the model.

I'm not sure I agree with your first point.
Logical validity is defined by quantifying over all models, 
by Tarski. Validity is not *absolute*?

Secondly, atomic formulas do not have a definite truth value within
the model. They have truth values *under an assignment*.
A formula can only have a definite truth value in your sense
if its universal closure is true, or if the universal closure
of its negation is false. 

Peter Ladkin