由"let"帶頭的祈使句(Imperative Sentences)是個常見的動詞句型，它的主要用法有下列三種：
1.表示“建議”。
這個句型里的"let"后頭緊跟著一個第一人稱的代詞賓語，如：
(1) Let me try.
(2) Let's do it.
(3) Let me go and look for it.
這個句型語氣委婉，比直接的祈使句客氣。試比較(4)a和(4)b:
(4) a. Don't disturb him.
b. Let's not disturb him.
(a)是直接命令，語氣強烈，不如(b)溫柔悅耳。
2.表示“間接命令”或“愿望”。
這句型里的動詞賓語是第三人稱名詞或代詞，如：
(5) Let Robert take charge of the marketing department.
(6) Let her join our choir.
3.表示“警告”、“蔑視”、“威脅”等。
這種祈使句里的賓語也是第三人稱為主。除了口氣兇悍之外，有時還語帶諷刺，如：
(7) Let him try and he will expose his inability to work on his own.
(8) Let the invaders come and our armed forces will wipe them out in no time.
用"let"的祈使句時，必須注意下列幾點：
一、"let" 的否定句有二。如果賓語是第三人稱用"Don't let....."(見例(9));如果賓語是第一人稱，則用"Let......not" (見例(10))：
(9) Don't let this type of things happen again.
(10) It's raining now. Let's not go out until after the rain.
二、"Let"只適用于現(xiàn)在時態(tài)，可以有被動語態(tài) (the passive voice)，如：
(11) Let the recalcitrant criminals be sent to prison.
(12) Let all the dedicated capable staff be promoted.
三、"Let"后頭除了是不帶"to"的不定式動詞 (The infinitive without"to")之外，還可以是某些適當?shù)母痹~，如out, in, down, alone等：
(13) Let the puppy out.
(14) Open the windows and let the fresh air in.
(15) The room is too sunny. Let the blinds down.
(16) Let me alone, please.
四、用"Let's"時，把談話者的對象包括在內;用"Let us"時，并不包括對方，如：
(17) Let's try it, shall we?
(18) Let us do it by ourselves, will you?
從(17)里的"shall we"和(18)里的"will you"，不難知道前者包括聽話人，后者并沒有。
