The term 'tense' can be defined as a secondary grammatical category which serves to locate an event or a situation in time. It accounts for example for the difference in the sentences ‘John leaves’ or ‘John left’. It encompasses two aspects: a morphological aspect, namely a system of tenses encoded in the verb's morphology, and a semantic aspect dealing with the temporal location of the event or events depicted in one or more sentences: the 'meaning' of the various tenses.