 Triadic Logic is that logic, which though not rejecting entirely the Principle of Excluded Middle, nevertheless recognizes that every proposition, S is P, is either true or false, or else has a lower mode of being such that it can neither be determinately P, nor determinately not-P, but is at the limit between P and not P. (Ms 339, copied from Fisch &amp; Turquette 1966: 75)