There are several axiomatic systems of [temporal logic](http://en.wikipedia.org/wiki/Temporal_logic) (aka tense logic). You can find more e.g. in Hodkinson and Reynold’s chapter in the Handbook of Modal Logic, in [this introduction](http://staff.science.uva.nl/~yde/papers/TempLog.pdf) by Venema, or, from a more philosophical standpoint, in [SEP](http://plato.stanford.edu/entries/logic-temporal/).