 Apart from absolute tense—exemplified by (1a)–(1c)—where the reference point from which the location in time is evaluated is the present, there is also  relative tense where the reference point is not necessarily the present but may be given by context. Thus in a sentence like The student had worked on his thesis the student’s work took place at a time before a reference point in the past, in contrast to (1c) where the reference point is the present. Other instances of relative tense in English are the present perfect and the future perfect in (2a) respectively (2b). 