Performing a Super Search on titles of 'truth', I got What is truth? (Curiosity corner) which is robin's attempt to talk at great length about this. That may help. That wasn't the one I was looking for, so again with the Super Search - this time on text of 'truth table', where I found bobf's True or False? A Quick Reference Guide. That, too, may help, although I think robin's was a bit more of a gem find.

Random node walking ... via Super Search. Fun. :-)