Patterns Of Time In English: Tense

Halliday & Matthiessen (1999: 215):

English foregrounds location in the flow of time (tense), and construes this not only as past/present/future relative to 'now' [they paid me/they pay me/ they will pay me], but also as past/present/future relative to some moment that is relative to now [they are going to pay me (future in present), they've been paying me (present in past in present)], with the possibility of up to five shifts of reference point, as in 

They said they'd been going to've been paying me all this time …

(present in past in future in past in past). This system is fully grammaticised, and is unusual in that it construes location in time as a logical relation rather than as an experiential taxonomy; it thus becomes a form of serial time reference. The tense categories also combine with time adverbs such as already, just, soon [they'd already paid me, they've just paid me, they soon paid me]. Interestingly, the deictic time reference (that appealing to 'now') can be switched off; either there is no deixis (the clause is non-finite, e.g. not having paid me yet...) or the deixis takes the form of modality (speaker's angle on the process, e.g. they should have paid me).