用来体现说话者对其所言的主观态度的句法
表示情绪，态度，推测
情态动词+ 动词原形
没有人称的变化
时态变化有限(现在时和过去时)
| 现在时 | 过去时 |
|---|---|
| must | 无 |
| can | could |
| will | would |
| shall 若表示将要，用与第一人称 | should |
| may | might |
could would should might 可以现在时使用，比较委婉
必须
we must also tread with caution
Scientists must communicate their message to the public in a compassionate, understandable way
能够，可以
and the right mental workouts can significantly improve our basic cognitive functions.
Similarly, the physical act of laughter could improve mood.
愿意，将要
Will you marry me?
The first draft will appear on the page.
Potential home buyers would cheer for lower interest rates.
可以 可能， 每个情态动词都可以表示推测
expressions may influence emotions rather than just the other way around.
Such bodily reaction might conceivably help moderate the effects of psychological stress.
The details may be unknowable
应该
America should follow.
Those suffering from persistent nightmares should seek help from a therapist.
the peculiar way of conducting the experiments may have led to misleading interpretation of what happened.
Now something similar could be happening in the oceans.