在肯定句中用实意动词,疑问句和否定句中随便用.例如：
You need to hand in your homework tomorrow.
Do you need to hand in your homework tomorrow?
Need you hand in your homework tomorrow?
You don't need to hand in your homework tomorrow.
You needn't hand in your homework tomorrow.
但是以物作主语时,一般不用于情态动词.
如：
The flower needs watering.=The flower needs to be watered.