This unit offers an overview of modal verbs in the past tenses. The past tense of modal verbs varies depending on the verb. Here is a short list of modal verbs with their past tense forms:
can = could, was/were able to
must = had to
may = might, was/were allowed to
used to = used to
ought to = ought to
will = would, was/were going to
shall/should = should, was/were supposed to
Examples:
Laura was able to lift the heavy box.
Jerry had to go to work.
The children were not allowed to run inside the house.
I used to run five miles every day.
He was going to ask about the price of a new laptop, but he forgot.
You were supposed to do your homework.
Note that the base form of the main verb is used in each of the above examples (with “to” after forms such as had to, was able to and used to), and occurs after the past tense form of each modal verb.
It is important to note some forms that include the modal verbs in the past are actually reported speech, subjunctive mood or conditionals, and should not be confused with the past simple. Take a look at the following sentence:
Bob said that he would be here at 8:00.
In this example, the use of would is the past simple form of the modal verb will, but it functions as reported speech and leaves open whether Bob actually arrived. The actual sentence uttered by Bob might have been, “I will be there at 8:00.” It could be something that was uttered in the present (potentially before or after 8:00) or the past, but there is too little information to know for sure.
Some modal verbs do not have stand-alone simple past forms, but instead, they look more like the present perfect, in that they use the auxiliary verb “have” and the past participle of the main verb. These modal verbs include: could, should, would, may, might, and must.
Examples:
We would have finished the project if we hadn’t run out of time.
They could have been nicer to us.
You should have told him about the delay.
In the first example, the third conditional – an unrealistic or hypothetical situation in the past – is used. The second and third examples are not subjunctive: could have expresses a possibility that did not happen, and should have expresses criticism or regret about the past.