 By iterative uses of the \(Y\)- and \(T\)-operators we may define operators corresponding to the past and the future as \(Y^n\) and \(T^n\), respectively, where \(n\) is an arbitrary natural number. Obviously, this may be done with an arbitrary choice of time unit, i.e., \(T(p)\) and \(Y(p)\) could simply stand for “at the next moment it will be the case that \(p\)” and “at the moment just before now it was the case that \(p\)”, respectively. A logic of this kind appears to be based on time conceived as a linear series of discrete moments, but Prior pointed out that we may find this sort of discrete tense-logic attractive without committing ourselves to a strong metaphysical stance regarding time as such: 