 Of course, it is straightforward to modify the translations \(\mathrm{ST}_a\) and \(\mathrm{HT}\) above such that translations are obtained between hybrid tense logic (including the \(\mathtt{\forall}\) binder) and first-order logic with equality. The first-order logic under consideration is what Prior called first-order earlier-later logic. Given the translations, it follows that Prior’s first-order earlier-later logic has the same expressive power as hybrid tense logic.