Ken Hanly
Fri, 30 Jun 2000 22:11:49 -0700
This is all mixed up, mostly incorrect. Some types of tautology are true because of definitions. The types of tautologies recognised by philosophers such as Kant. "All bachelors are unmarried" As Kant puts it the predicate "unmarried" is included in the definition of "bachelor". One could say that these sorts of statements are in a sense true by definition. However a tautology such as "It is raining or it is not raining" is not true by definition in any straightforward way. It is true because of the manner in which the truth functional operators "not" and "or " work to form compound propositions. The fact that something you write down is a tautology (or a contradiction) does not relieve one of any burden of proof. Writing down "It is raining or it is not raining" does not prove it is a tautology and the fact that something is true does not show that it is a tautology. One has to prove that it is a tautology. For example by constructing a truth table. A tautuology is not simply true. It is necessarily true or true for formal reasons not because of empirical facts. Cheers, Ken Hanly Rod Hay wrote: > Yes, of course, Charles. > > Rod > > Charles Brown wrote: > > > >>> [EMAIL PROTECTED] 06/30/00 01:25PM >>> > > After thinking better of my sarcastic tone to Carrol's message. Let me > > explain. > > > > A tautology is a statement that is true by definition. That is, it is > > always true. > > > > A = A is a tautology. > > > > A = B is not a tautology. That is, it might be false. > > > > Similarly all true statements are not tautologies. I.e., A = B might be > > true. > > > > __________ > > > > CB: Sorry, couldn't help saying this since we are in a logical vein. You mean "not >all true statements are tautologies" , I believe. > > > > I agree with your post, though. > > > > _________ > > > > If all statements were tautologies, math and logic would be very easy. > > Anything you write down would be true. No need to prove anything. > > > > -- > > -- > Rod Hay > [EMAIL PROTECTED] > The History of Economic Thought Archive > http://socserv2.mcmaster.ca/~econ/ugcm/3ll3/index.html > Batoche Books > http://Batoche.co-ltd.net/ > 52 Eby Street South > Kitchener, Ontario > N2G 3L1 > Canada