<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META content="text/html; charset=iso-8859-1" http-equiv=Content-Type> <META content="MSHTML 5.00.2722.2800" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT face=Arial size=2>I dont understand. Both modus ponens and modus tollens are valid. There is no question of testing their validity except aa an exercise for students in constructing truth tables. Are you talking about soundness?</FONT></DIV> <DIV> </DIV> <DIV><FONT face=Arial size=2>Cheers, Ken Hanly</FONT></DIV> <BLOCKQUOTE style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px"> <DIV> <P>I agree with P that in general, a strong intuition trumps an apparantly strong argument for a counterinituitive conclusion. It's a pragmatist platitude taht one man's modus ponens is another man's modus tollens, that if an argument has an unpalatable conclusion, we might do well to reassess the truth of the premises and test the validity of the reasoning. This is also Rawls' view. It is the basic idea that the notion of reflective equilibrium i supposed to capture.</P> <P>--jks</P></DIV><BR clear=all> <HR> Get your FREE download of MSN Explorer at <A href="http://go.msn.com/bql/hmtag_itl_EN.asp">http://explorer.msn.com</A><BR></BLOCKQUOTE></BODY></HTML>