  Another possibility is that the particular I form might be true when its subject is empty.  This was a common view concerning indefinite propositions when they are read generically, such as ‘A dodo is a bird’, which (arguably) can be true now without there being any dodos now, because being a bird is part of the essence of being a dodo.  But the truth of such indefinite propositions with empty subjects does not bear on the forms of propositions that occur in the square.  For although the indefinite ‘A dodo ate my lunch’ might be held to be equivalent to the particular proposition ‘Some dodo ate my lunch’, generic indefinites like ‘A dodo is a bird’, are quite different, and their semantics does not bear on the quantified sentences in the square of opposition. 