要求对方或希望对方允许自己或他人做什么或不做什么的句子才叫祈使句.
祈使句有两种基本结构：
1、直接用动词原形陈述的祈使句表示向提对方出要求.如：Mind your own business, please.Come and have dinner with us.Stay behind!2、用 let 开始的祈使句表示希望对方允许自己或他人做某事.如：Let’s go.Let me drive you home.Let them keep quiet.
以上述基本结构为基础可以衍变出以下几种委婉的祈使语气：
第一种结构的衍变
1）附加will you?, won’t you? 或would you? 问句Mind your ownbusiness, will you?Come and have dinner with us, would you?Stay behind, won’tyou?2）将will you, won’t you 或 would you 放在句首Will you please mind your own business?Would you (please) come and have dinner with us?Won’t you stay behind?3）用wish 或 if 变成虚拟语气I wish you could mind your own business. 但愿你能管好你自己.I wish you could come and have dinner with us. 你能来与我们一起共进午餐该多好.If you could stay behind! 要是你能留下来就好了.
第二种结构的衍变
1）附加shall I (we, he, she, they)Let’s go, shallwe?Let me drive you home, shall I?Let them keep quiet,shall they?2）去掉let,把 shall I (we, he, she, they) 放到句首Shall we go?Shall I drive you home?Shall they keep quiet? You will mind your own business 不符合上述结构,所以不是祈使句.