By Schubert Ogden
...
It may mean either of two things: either that x presupposes, in the sense that x requires y by a specific and definite necessity:, or that x anticipates y, in the sense that x requires y by only a generic and indefinite necessity. (Perhaps another way of explaining what is meant by the two things that implication may mean-- —i.e., presupposition and anticipation--is anticipation—is to say that, whereas the implication rightly distinguished as "presupposition" is unconditional, the implication rightly distinguished as "anticipation" is conditional.)
...