  Early in the twelfth century Abelard objected to Boethius’s wording of the O  form,[8]  but Abelard’s writing was not widely influential, and except for him and some of his followers people regularly used ‘Some S is not P’ for the O form in the diagram that represents the square. Did they allow the O form to be vacuously true? Perhaps we can get some clues to how medieval writers interpreted these forms by looking at other doctrines they endorsed.  These are the theory of the syllogism and the doctrines of contraposition and obversion.