0 used to refer to a situation in which there is a choice between two different plans of action, but both together are not possible: --
I do not think that this is an either-or situation.
As he said, it is not an either-or situation.
It is important that there should be an either-or choice.
There seems to be an either-or attitude in the matter.
So it is not a case of either-or, because you cannot have one without the other.
That is to say, knowing a word is quite often not an either-or situation; some words are known well, some not at all, and some are known to varying degrees.
While the grammar extensively discusses the problematic borderlines between categories, in the end an either-or choice is made, and elements are assigned to one class or another.
Often pulling in opposing directions, the day-by-day resolution of these tensions generates differing degrees of change in a variety of ways, rather than generating strictly dichotomous either-or outcomes.
