动词在充当谓语时,其形式受到主语的限制;谓语的形式要和主语在人称和数上保持一致。这种形式称为动词的限定形式(Fi-nite Forms of the Verb),该形式表现出:
人称(Person)——与主语在人称上保持一致:
I'm not late,am I? 我没迟到,是不是? (第一人称单数)
Where is John? 约翰到哪里去了? (第三人称单数)
Are you John's brother? 你是约翰的兄弟吗? (第二人称单数)
数(Number)——与主语在数上保持一致:
He who laughs last laughs longest.(谚)谁笑在最后,谁笑得最久。(第三人称单数)
My brother and sister are here. They visit every week.我的兄妹来了,他们每周都来访。(第三人称复数)
Do we have the right to destroy the world in which we live? 难道人们有权利去破坏我们所生活的这个世界吗? (第一人称复数)
时态(Tense)——表示动作发生的时间:
Where did you go yesterday? 昨天你到哪儿去了? (过去时)
I went to see a friend of mine.我去看了一位朋友。(过去时)
The sun rises in the east.太阳从东方升起。(一般现在时)
Are you going to have dinner at home tomorrow night? 明天晚上你准备在家吃晚饭吗? (将来时)
语态(Voice)——表示主语是做这动作的人或物还是承受动作的人或物:
Their mother punished them for their rudeness.母亲因为他们态度粗鲁而责罚他们。(主动)
He was severely scolded by his mother.他被母亲严厉地训斥了一顿。(被动)
Motorists should be severely punished for dangerous driving.危险驾驶的开车人士应受到严惩。(被动)
语气(Mood)——表示说话人认为这句话是事实,还是要求做的事或假想虚拟的事:
Today is Monday.今天是星期一。(陈述事实)
Come here and look at this.到这儿来,看看这个。(提出要求)
I wish I were a bird.我要是只鸟就好了。(表示愿望)
动词是一个句子的重心,因此从动词的变化,可以了解动词的时态,看出该句是现在时、过去时还是将来时;亦可从动词的变化,了解动词的语态如主动还是被动;还可了解动词的语气等。
助动词与实义动词(有些语法书称之为完全动词)连用,表示动作或状态的其他情况,如助动词be可与完全动词的现在分词连用,表示动作在某一具体时间内正在进行(如:He was swimming.他在游泳);助动词have可与完全动词的过去分词连用,表示动作已经完成(如:I have finished.我做完了。)。
动词还有一种不受主语限制的形式,称为动词的非限定形式(Non-Finite Forms of the Verb)。该形式不能独立作谓语,但可以和助动词或情态动词等构成谓语,在句中充当主语、宾语、定语、状语、表语等。英语有三种非限定形式:
动名词(the Gerund):主要起名词的作用,可以作主语、宾语和表语等:
Seeing is believing.(谚)眼见为实。(作主语)
The children amused themselves by playing games.孩子们做游戏取乐。(作介词宾语)
Keep going till you reach the traffic lights.你可以一直往前走,到交通灯那里为止。(作宾语)
分词(the Participle):分词有现在分词和过去分词两种。现在分词和动名词的形式相同。分词主要起形容词和副词的作用,可以作定语、表语和状语等:
They use computers to keep the traffic running smoothly.他们用计算机控制交通,使车辆畅通无阻。(现在分词作宾补)
He reacted with surprising speed.他以惊人的速度做出了反应。(现在分词作定语)
Her narrow escape left her feeling shaken.她险些丧命,事后仍感到心有余悸。(过去分词作宾补)
He has an exaggerated idea of his own importance.他自视过高。(过去分词作定语)
不定式(the Infinitive):既起名词作用,又可起形容词、副词的作用,可以作主语、宾语、定语、表语和状语等:
It was difficult for us to decide which one to buy.(对我们来说)难以决定买哪一个。(作主语)
I don't know how to swim.我不会游泳。(作宾语)
My dream is to become a scientist.我的梦想就是成为一名科学家。(作表语)
My parents are coming to have dinner with us.我父母来同我们一起吃饭。(作状语)