White is black

Lately, Bill is wrestling with medieval modality.  I have trouble understanding modern modal ideas so I rather doubt my ability to penetrate their medieval predecessors.  Let me just comment on something that Bill says a propos a paper by Marilyn McCord Adams:

Adams writes, p. 39, "(Ockham is willing to conclude that 'A human supposit can be assumed' is true, even though 'A human supposit is assumed' is contradictory; just as 'A white can be black' is true,  even though 'A white is black' is impossible.)"

My present purpose is to make sense of this quotation. I give 'A white can be black' a de re reading as follows:

1. A white thing is (logically) possibly such that it is not white.

For example, here is a piece of white paper.  Heeding Mick Jagger's injunction, I can paint it black.  But I wouldn't be able to do this if it were not logically possible for this thing that is actually white to be non-white. Although, necessarily, nothing white is non-white, the piece of paper is contingently white.  I give 'A white is black' a de dicto reading:

2. It is not (logically) possible that a white thing be non-white.

On these readings, both (1) and (2) come out true.  (1) is about a thing (res) and ascribes a modal property to it; (2) is about a proposition (dictum) and ascribes a modal property to it.

Bill is claiming, I think,  that though (1) and (2) at first glance look contradictory they are in fact both true and that this is due to a subtle distinction between the scopes of the possibles and the nots.  But I'm not at all sure that he has dispatched the ambiguities.   Indeed, I fear he has muddied the waters further with talk of 'modal properties' of things and of propositions.  For I can read both (1) and (2) as false.  I read (1) as

1*.  Possibly, some white thing is not white,

and I read (2) as

2*.  Not Possibly, some white thing be not white.

The critical distinction for me is the mood of the copula.  In (1*) it's indicative and in (2*) it's subjunctive.  Note that in both cases I have retained the is and the be that Bill uses.  To my ear the is in (1*) roots us in the present, whereas the be in (2*) ranges over past, present, and future. Surely no thing that is white now is anything other than white now, whereas a thing that is contingently white may have been other than white in the past and may be so in the future.  

This is all highly problematic for the practice of philosophy.  Bill and I agree that there are distinctions of sense to be made here, and we agree what those different senses are, I think.  But we use rather different language to express those senses.   Has no Quine come forward to regiment these usages?  Maybe after all there is no general agreement as to the distinctions of sense that need to be made. Bill and I have disagreed about much, including the present tense!