Full Idea
We introduce four future and past tense operators: FP: it will sometime be the case that P. PP: it was sometime the case that P. GP: it will always be the case that P. HP: it has always been the case that P. (P itself is untensed).
Clarification
[F, P, G and H are in bold]
Gist of Idea
F: will sometime, P: was sometime, G: will always, H: was always
Source
M Fitting/R Mendelsohn (First-Order Modal Logic [1998], 1.10)
Book Reference
Fitting,M/Mendelsohn,R: 'First-Order Modal Logic' [Synthese 1998], p.25
A Reaction
Temporal logic begins with A.N. Prior, and starts with □ as 'always', and ◊ as 'sometimes', but then adds these past and future divisions. Two different logics emerge, taking □ and ◊ as either past or as future.