Past Forms
The preterite (past) forms given above (could, might, should and, would, corresponding to can, may, shall and will respectively) do not always simply modify the meaning of the modal to give it past time reference. The only one regularly used as an ordinary past tense is could, when referring to ability: I could swim may serve as a past form of I can swim.
All the preterites are used as past equivalents for the corresponding present modals in indirect speech and similar clauses requiring the rules of sequence of tenses to be applied. For example, in 1960 it might have been said that People think that we will all be driving hovercars by the year 2000, whereas at a later date it might be reported that In 1960, people thought we would all be driving hovercars by the year 2000.
This "future-in-the-past" usage of would can also occur in independent sentences: I moved to Green Gables in 1930; I would live there for the next ten years.
In many cases, in order to give modals past reference, they are used together with a "perfect infinitive", namely the auxiliary have and a past participle, as in I should have asked her; You may have seen me. Sometimes these expressions are limited in meaning; for example, must have can only refer to certainty, whereas past obligation is expressed by an alternative phrase such as had to (see Replacements for defective forms below).
Read more about this topic: English Modal Verbs
Famous quotes containing the word forms:
“Our normal waking consciousness, rational consciousness as we call it, is but one special type of consciousness, whilst all about it, parted from it by the filmiest of screens, there lie potential forms of consciousness entirely different.”
—William James (1842–1910)
“I may not tell
of the forms that pass and pass,
of that constant old, old face
that leaps from each wave
to wait underneath the boat
in the hope that at last she’s lost.”
—Hilda Doolittle (1886–1961)