 The standard translation discussed in the previous section links the semantics of Prior’s basic tense logic to first-order logic. Yet, there are crucial differences between the two approaches to formalizing the logic of time. In fact, in the early days of temporal logic, Prior’s approach was perceived as a rival to more conventional approaches using first-order logic. The rivalry between tense logic and first-order logic can be seen as reflecting a fundamental distinction concerning the nature of time, namely the distinction between the A-series and the B-series of time introduced by McTaggart (1908).