B2 · Lesson 26 · 25 min
Modals about the past
In this lesson
- I can distinguish past deductions, criticism and unnecessary completed actions.
- I can form modal perfect structures and explain how the modal changes the meaning.
Grammar in context
The lights were still on when we arrived. Someone must have forgotten to switch them off. We should have checked before leaving. We needn’t have bought extra torches, because the caretaker had already supplied some.
Which sentence makes a deduction, which criticises an earlier decision, and which says an action happened unnecessarily?
Infer or allow a past possibility
Use must have plus a past participle for a strong deduction about a past event. May have, might have and could have can present possibilities, while cannot have or can’t have can express a strong negative deduction. The perfect form places the event before the reference point, but the modal tells the reader how the speaker judges it. These are inferences or possibilities rather than direct evidence that the event occurred.
- She must have left the keys at work; they are not here.
- The email might have gone into the spam folder.
Evaluate a past choice
Should have plus a past participle often criticises a missed action or expresses regret about what was advisable. Should not have can criticise an action that did occur. Could have can describe an unused opportunity or ability, so it does not always mean an uncertain deduction. Context identifies the intended reading. Do not confuse must have left, a deduction, with had to leave, which describes a past requirement.
- We should have checked the opening times.
- I could have borrowed a bike, but I chose to walk.
An unnecessary action that happened
Needn’t have plus a past participle says that an action was performed but was unnecessary. Did not need to describes the absence of necessity and does not, by itself, tell us whether the action happened. Keep that distinction when interpreting a sentence. All these modal perfect forms use have rather than has, even with singular subjects, and use a past participle rather than a past simple form.
- You needn’t have printed the tickets; the digital version was enough.
- We didn’t need to print tickets, so we left the printer switched off.
Common mistakes
Compare the incorrect and corrected forms.
Avoid
She must have went home.
Use
She must have gone home.
A modal perfect requires a past participle after have.
Avoid
He should has checked the address.
Use
He should have checked the address.
A modal is followed by base-form have, regardless of the subject.
Put it into practice
Try the exercises, write your own examples and check your understanding.