情態(tài)動(dòng)詞也可以和動(dòng)詞進(jìn)行形式或完成進(jìn)行形式構(gòu)成謂語：表示“應(yīng)當(dāng)正在……”，“想必正在……”的意思。
【例如】
Why should we be sitting here doing nothing?
She might still be thinking about the question you raised.
He can't be swimming in such weather.
At the moment she may (might) be playing with her schoolmates.
We needn't be standing here in the rain. We might take shelter in the hut over there.
情態(tài)動(dòng)詞間或也可以和一個(gè)動(dòng)詞的完成進(jìn)行形式構(gòu)成謂語，表示“應(yīng)當(dāng)一直在……”，“想必一直在……”這類意思。
【例如】
They are sweating all over. They must have been working in the fields.
They may have been discussing the problem this morning.
She couldn't have been swimming all day.
