Learn English – “has been” vs “have been”

auxiliary-verbsgrammaticalitymodal-verbsverb-agreement

I am answering an online English grammar test and encountered the following question

Where was Jack yesterday? —I don't know. He ________ seeing the doctor.

My answer is: might has been
Correct Answer is: might have been

Why not might has been? He is singular?

Best Answer

Because the verb is "might". After the first verb you use the infinitive, for example:

He has something.

He might have something.

The same rule applies when using "have" to indicate past tense. I will bold the conjugated verbs in the following examples. The following verbs are in infinitive forms.

He is sick.

He has been sick.

He might have been sick.

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