情态动词无人称和数的变化,情态动词后面跟的动词需用原形,否定式构成是在情态动词后面加 "not"。个别情态动词有现在式和过去式两种形式,过去式用来表达更加客气,委婉的语气,时态性不强,可用于过去,现在或将来。 He could be here soon. 他很快就来。 We can't carry the heavy box. 我们搬不动那箱子。 I'm sorry I can't help you. 对不起,我帮不上你。
基本助动词与情态助动词最主要的区别之一是:基本助动词本身没有词义,而情态助动词则有自己的词义,能表示说话人对有关动作或状态的看法,或表示主观设想:
What have you been doing since? (构成完成进行体,本身无词义) I am afraid I must be going. (一定要) You may have read some account of the matter. (或许已经)
除此之外,情态助动词还有如下词法和句法特征:
1) 除ought和used以外,其他情态动词后面只能接不带to的不定式。如果我们把ought to和used to看做是固定词组的话,那么,所有情态动词无一例外地只能接不带to的不定式: We used to grow beautiful roses. I asked if he would come and repair my television set. 2) 情态助动词在限定动词词组总是位居第一: They need not have been punished so severely. 3) 情态助动词用于第三人称单数现在时的时候,没有词形变化,即其词尾无-s形式: She dare not say what she thinks. 4) 情态动词没有非限定形式,即没有不定式和分词形式,也没有相应的动名词: Still,she needn't have run away. 5) 情态助动词的“时”的形式并不是时间区别的主要标志。在不少场合,情态助动词的现在时和过去时形式都可以表示现在、过去或将来时间: Would you mind very much if I ask you to do something? She told him he ought not to have done it. 6) 情态助动词之间是相互排斥的,即在一个限定动词词组中只能出现一个情态助动词,但有时却可以与have和be基本助动词连用: You should have washed the wound. Well,you shouldn't be reading a novel. |