Tht the future must be true, which can be pretty difficult to do
because -- well -- the future is unknown.
Due to the unpredictable nature of the future (compared to the past
which is a collection of true or false or in between statements) maybe
all statements involving a future tense are somewhat already tensed
with a "in one or more worlds, possibly excluding this one" i.e.
[ka'e] under my interpretation of CAhA. Hm, I wonder if one of the
other CAhA has the interpretation "in one or more worlds, strictly
excluding this one" (where "this one" is "the world of dei"). Maybe
{nu'o}?