One of the most serious pre-occupations of post-medieval philosophy has been to distinguish those kinds of assertion which are either true or false from those which are neither true nor false. A solution to this problem would be of the highest importance. It would indicate in what areas rational inquiry has some hope of success and in what areas it is doomed to frustration. It would tell us, for example, whether it is worth trying to think about the possible mistakenness (...) of our moral principles, or whether such thinking is bound to be ineffective since no truth or falsity attaches to them. (shrink)