oncrete syntaxes.
&gt; 
&gt; And by the way, the basis for model theory was stated by Aristotle,
&gt; developed in detail by the medieval Scholastics, and adopted by Peirce
&gt; to demonstrate the soundness of his rules of inference for existential
&gt; graphs.  In his famous paper, Tarski acknowledged Aristotle, but he
&gt; had to fight a hard battle against Frege's claim that truth was too
&gt; vague a concept to be used as a basis for logic.  That is just one
&gt; point I make when I try to inform logici