The expression of grammatical time/tense (Lat. tempus) constitutes the basis of the verbal category of finitude (the division of all the forms of the verb into finite and non-finite). The category of tense is a verbal category that reflects the objective category of time.
The essential characteristic of the category of tense is that it relates the time of the action, event or state of affairs referred to in the sentence to the time of the utterance (the time of the utterance being ‘now’' or the present moment). The tense category is realized through the oppositions. The binary principle of oppositions remains the basic one in the correlation of the forms that represent the grammatical category of tense. The present moment is the main temporal plane of verbal actions.
In Modern English, the grammatical expression of verbal tense is effected in two stages:
1) the process receives an absolutive time characteristic by means of opposing the past tense to the present tense. The marked member of this opposition is the past form (retrospective evaluation of the time of the process)
2) At the second stage, the process receives a non-absolutive relative time characteristic by means of opposing the forms of the future tense (strong member) to the forms of no future marking (prospective eva,uation of the time of the process).
Therefore two temporal categories are distinguished: 1) the category of primary time, 2) the category of prospective time.