Ex. 1- Degrees of Probability in Past Time: must have, may have, might have, could have, had to have

Instructions. Complete the sentences. Use the words in parenthesis to complete the sentence in past time.
Example:
Roger: You (must, be) _______________surprised when you found out about the salary increase.
George: Yes, I was very pleasantly surprised.

must have been

Explanation

The following forms express degrees of probablity of an action or condition that occurred or did not occur in the past.

1. Joseph had to have known about the plan to sell the company.
The speaker is 100% certain that Joseph knew about the plan. This is sometimes referred to as a logical conclusion.

2. Joseph must have known about the plan to sell the company.
The speaker believes that it is almost certain that he knew. This is sometimes referred to as a logical conclusion.

3. Joseph could not have known or couldn't have known about the plan to sell the company.
The speaker is 100% certain that Joseph did not know about the plan, an example of a logical conclusion in the negative.

4. Joseph might have known about the plan to sell the company.
The speaker believes that there is about a fifty-fifty chance that Joseph knew.

5. Joseph may have known about the plan to sell the company.
The speaker believes that there is about a fifty-fifty chance that Joseph knew.

6. Joseph could have known about the plan to sell the company. .
The speaker believes that there is about a fifty-fifty chance that Joseph knew.

May have, might have, and could have have the same meaning. All three express about a fifty-fifty probability that an action or condition occurred (see 4-6).

Click here to see a list of past participles.