I have been leafing through Ueberweg's System of Logic, which is an interesting nineteenth-century and Teutonic look at that subject. Very few logic text books would now mention Hegel's logic, for example. He has an interesting discussion of the principle of Excluded Middle, the one that says any sentence, or its negation must be true. He claims (p. 263) that the principle may be invalid in certain instances. For example, 'not proven' fills an obvious gap between 'guilty' and 'not guilty'.
Surely not. What does 'not proven' mean? It means not proven to be guilty. 'It is proved that' is an operator on the proposition 'x is guilty', not a third truth value filling the gap between sentence and negation. What an elementary mistake, or have I missed something?