It must be understood that a proposition about the future can be understood to signify something in the future in two ways. So that the proposition about the future signifies it to be true now that something in the future will have to be true [verum esse habebit] (for example, that ‘you will be white at a’ signifies it now to be in reality so that at time a you will be white). Or it can be understood that it signifies now that you will be white then: not that it signifies that it is now such that then you are going to be white, but that it signifies now that then you will be white. For to signify it to be [the case] now that you will be white at a, signifies more than to signify that you will be white at a.
So Scotus notes two possible ways of talking about the future:
1) I say what the future is determined to be: "It is now true that tomorrow you will be white".
2) I say something determinate about the future, which at the moment is indeterminate: "I am now saying that tomorrow you will be white", even if what is true now is that tomorrow you may be white or you may be red.
Saying that I think that things will turn out so-and-so is not the same thing as saying that there is something in reality now which determines that in the future things will be so-and-so, but that I think that, when the causal determinators determine how things turn out, they will end up making things so-and-so rather than such-and-such.
And we have to distinguish between statements like:
a) "In three years grass will still be green"
b) "In three years Obama will still be President of the U.S".
(a) is in one sense a future contingent. It may turn out in three years that there is no more grass, or that there is a massive drought and all the grass is yellow or brown. But "grass is green" will still be true in the sense that greenness will still belong to the essence of grass, even if no existing grass can actualize that essential property due to accidental circumstances. (a) is really not a statement about a given moment or time period at all, but a statement about the nature of grass, which is invariant across all the times in which grass exists in its normal state. It's analogous to "A rose by any other name would smell as sweet", which taken by itself is not so much about nomenclature as about horticulture.
But (b) is different. Obama's being President will be a purely contingent fact, since it is not in the nature of anything for that to be the case, but will be due only to the aggregate of choices voters will by then have made. So when I (as I would if I were a pundit) say that Obama will or will not be President after the next election, I'm saying that I think most voters will end up making a certain choice; I'm not saying that (since the truth about the future is determinate) there will be no choices, or that they have already made their choices. Rather, every such projection carries with it the implicit caveat, "If current trends continue . . ."