表示请求、鼓励、建议、命令或警告时，常用祈使句。在祈使句中通常不用主语，谓语动词用原形，句末用句号或惊叹号。祈使句一般用降调。
[@more@]肯定式：Have a good time !
Be quiet !
Let's begin the work .
否定式：Don’t take the pen away .
Don't be so slow .
Never be late .
Let's not waste time .
为了加强祈使句的语气，可以在动词前加助动词do .
Do come again .
Do sit down .
Do be careful !
要慎用祈使句,因为祈使句会给人以口气生硬的感觉.为缓和语气,可以使用其他结构,有礼貌地提出要求,如:Please could you…,If I were you,I’d…,Could you…,please等。例如：
Open the door, could you?
Please could you open the door?
Could you open the door, please?