An objective and relational theory of local time is expounded and its philosophical implications are discussed in Sect. 2. In Sect. 3 certain physical and metaphysical questions concerning time are taken up in the light of that theory. The basic concepts of the theory are those of event, reference frame, chronometric scale, and time function. These are subject to four axioms: existence of events, frames and scales; time is a real valued function; the set of events is compact; and any (...) duration can be subdivided into two contiguous durations. Several theorems are derived, among them the one of the asymmetry of time. And a number of concepts are defined, such as those of time order, instant, and time coordinate. It is argued that the theory, though untestable, belongs to the background of a number of scientific theories. It is also shown that it includes all relational theories of time. The usual confusion between the asymmetry of time and the direction of irreversible processes is clarified. Time reversal is interpreted either as a purely formal operation or as a convenient way of describing motion reversed processes. Time orders are shown to be both relative and objective, apart from the choice of the positive direction, which is conventional. The various attempts to define the direction of time in terms of irreversible processes are shown to be logically untenable and methodologically undesirable. A number of metaphysical questions, such as the one of the reality and the fundamental character of time, are tackled. Finally the occasion is seized to extoll the advantages of systematization over both ordinary language discussions and open context analyses. (shrink)