This is the sixth of 17 posts, which are collectively Eternity, etc.
......Ordinary language is vague (see previous post), and the main thing here is that indefinite is not an unreasonable original truth-value under Presentism (given libertarianism), as follows.
......Under Presentism there would have been, before reading on, or not, those two (metaphysical) possibilities for how things could have turned out, not just the one (actual) future. So your belief about the future would not originally have concerned anything definite (insofar as your belief concerned the future directly, rather than via your intentions). The future is not completely definite under Presentism [i]; or in other words, the Presentist future is not completely real, in the sense that not all the statements about it that will ever have been correct are now true.
......As aforementioned, the future might be partially real—be what Mawson calls “real”—under Presentist Open Theism, because then it might be false (see section IV) that “there aren’t any true statements concerning future states of affairs at all”[ii]. However, the reason given by Mawson for the future being real was that some future contingency will either happen or not, and that if “we assume for the sake of argument that [it will] then that’s a fact about the future that someone could in principle have beliefs [about]”[iii]. And while it will either happen or not, as a matter of logic [iv], to presume that one of those two is already a fact is to reject (or ignore) the following picture of Presentist time, as dynamically branching.
......Presentists tend to picture the past as the trunk of a tree whose branches represent the future, one branch for each possible future [v]. If some future contingency does happen—and similarly if it does not—one could in principle look back down the single timeline of the past that includes it happening (or not), and see that fact with hindsight. Further back, and the contingency would definitely be going to happen (or not), but only with hindsight. At the time, it was one of two (metaphysical) possibilities.
......Since Mawson was right that Perfect Being Theists can, quite properly, be agnostic about theories of time [vi], and since the (logical) possibility of Presentism undermines—or at least reduces the significance of—his primary argument, the next section will further describe that possibility, and thereby answer three popular reasons for rejecting it.
......[i] The future is completely definite under 4-Dimensionalism (aka Eternalism); Michael Rea, “Four- Dimensionalism,” in Loux & Zimmerman, The Oxford Handbook of Metaphysics, pp. 246–80.
......[ii] Mawson, “Divine eternity,” p. 37.
......[iv] The ordinary meaning of “not” is all the logic we need here. The complicating factor is that, as aforementioned, “X will happen” can mean both that X will definitely happen and that X will, as it turns out, happen. Consequently “Either X will happen or else X won’t happen” is also ambiguous. For more discussion, see Rhoda, “Generic open theism,” p. 231.
......[v] For such pictures, see Denyer, Time, Action and Necessity, p. 12; Bourne, A Future for Presentism, p. 62.
......[vi] Mawson, “Divine eternity,” pp. 40–41.