1. 动词的屈折变化
什么是动词的屈折变化(inflection)呢？指的就是动词因时态、人称的不同而采用不同的形式，这种形式可能是词尾的变换，例如加后缀-ed、-d、-es、-s，-ing，等等；也可能不仅是词尾的变换，比如不规则动词的过去式和过去分词，这种变化可能是整个词都变换了，而不只是动词词干加后缀形式，例如leave过去式left、take过去式took、等等。
对于规则动词，加后缀后其发音变化分为以下三类：
(1) [id,d,t] (2) [ɪŋ] (3) [iz,z,s]
2. 动词屈折变换的应用(主要讲不规则的情况)
动词未产生屈折变化时的形式，我们暂且称其为动词词干(stem)，也有的称为根词(root)，或者我们称为原形动词。动词除了原形动词之外，还有另外三种形式，规则情况时分别对应前面的三种发音，不规则时要参见不规则动词表。
2.1 动词屈折变化可以充当的功能
用于引导谓语部分时，充当过去式(preterite，或者past tense；不用于引导谓语部分时，充当分词(participle)。
2.1.1 动词过去时态的应用
术语过去式(preterite)包括两种完全不相关的动词屈折变化功能：一种是过去时态(past tense)；另一种是情态形式(modal form)。
通常，动词“to be”动词是区分这两种功能的唯一手段：作为一种过去时态(past tense)和一种表达谦虚的过去式(a preterite of modesty)，“was”是单数第一人称的专用形式，其它情况下用“were”；“were”用于所有非现实性(irrealis)语境下，但是，在第一和第二人称单数时，也可以使用“was”替换，特别是英语口语中(colloquial English，或称“俗语”)。
动词是词性中唯一可以区分时间的部分。其它的词性部分可以在思想上与具体时间关联，例如名词表达一个行动；例如，“the conquest of Ireland”(征服爱尔兰)可以指当前、过去、或者未来。可以提到具体的时间：“Ireland in ancient times”；“English pronunciation in the 16th century”。但是名词没有表达时间区分的格式。
2.1.1.1 叙事体体表达的过去时态(Narrative Past Tense)
表达说话者认为在时间上完全区别于现在的，发生在过去的行动、或者所处的状态时，使用过去时态。这种情况，过去时态使用叙事体(narrative)。例如：
(1) Three hundred years ago the Pilgrim Fathers sailed for America in the Mayflower.
三百年前，朝圣者之父乘坐五月花号驶往美国。
(2) “But your house is not like that.”—“No, my house is all right; but it is the only dry house in the whole country round. I had it built on purpose.”
“但是你的房子不像那样”——“不，我的房子还可以；但它是全国唯一的干屋。我是故意建造的。”
2.1.1.2 描述体表达的过去时态(Descriptive Past Tense)
当使用过去时态描述一件过去经常重复发生的事时，使用描述体(descriptive)而非叙事体。这种迭代使用(iterative)与叙事体没有任何正式的区别，仅仅是这样使用使得含义清晰明了。例如：
(1) She spent the intervals of the London season in ragged schools and workhouses. When she went abroad with her family, she used her spare time so well that there was hardly a great hospital in Europe with which she was not acquainted.
她在破烂不堪的学校和济贫院度过了伦敦赛季的间歇。 当她和家人一起出国时，她充分利用了业余时间，以至于欧洲几乎没有一家她不熟悉的大医院。
(2) When Farmer Oak smiled, the corners of his mouth spread till they were within an unimportant distance of his ears; ...
农夫橡树微笑时，嘴角张开，直到离耳朵不重要的距离。
叙事体过去时态有时候用于对比过去和现在时间。例如：
(1) “Oh，you did give me a turn,” she exclaimed.
“I thought it was early for the milkman.”
“哦，你确实给过我机会，”她叫道。
“我以为送奶工还早。”
(2) A: I am sorry Mr. C. is not in. 很报谦，C先在不在。
B: I only called to see how he was. 我只是打电话来看看他怎么样。
(3) A: “Are you going to L. to-night?”“你今晚要去L吗？”。
B: “Why?” “怎么这么问呢？”
A: “Oh, I wondered.” “哦，我想知道。”
下面是一则体现时间的广告词：
Importance Notice. M.L. supplies all classes of domestic servants with good characters.
重要性通知。 M.L. 为各类家庭佣人提供良好品格。
We wondered where some of them got their good characters from.
我们想知道他们中的一些人从哪里得到了他们的好角色。
对于叙事体过去时态，当它用于表述不情愿(hesitation)时，有另一种专门的格式，即将想要表达的想法表述得非常遥不可及，从而表达自己的不情愿。例如，当某些事情发生使我们怀疑期望的正确性时，我们可以说，“I thought he was to lecture next week(我认为他下周要讲课)”。
假如一个作家希望脱离(dissociate)陈述事实，也常常有类似的用法。例如：
(Alexander) captured the cities of Susa and Persepolis—capitals and treasure-cities of the Persian king. One hundred and twenty thousand talents were said to have been obtained from the latter city.
(Alexander)占领了Susa和Persepolis——波斯国王的首都和宝藏城市。据说从后一个城市获得了十二万人才。
2.1.1.3 谦逊方式表达的过去时态(The Preterite of Modesty)
当过去时间的概念完全不存在时，遥远的过去时态会在不知不觉中导致这种情况。当我们说：“I called to ask you, if you would join us(我打电话问你是否愿意加入我们),” 过去时态的“would”似乎更有礼貌或者更为谦逊；它表明：我给你打电话陈述的是我的想法，但是现在，我想听听你的意见。我们按类似的方式使用过去时态：“I wanted to ask you if you would give a subscription(我想问你是否愿意订阅)。” Arnold Bennett先生在下面的一段文字中对这种谦逊过去时态(preterite of modesty)的使用进行了评论(Roll-Call,I ch. I§3章节)：
The young girl, opening the front door, had said:“ Do you want to see father?” And instantly the words were out George had realized that she might have said:“ Did you want to see father?”...in the idiom of the shop-girl or clerk , and that if she had said ‘did’ he would have been gravely disappointed and hurt. But she had not! Of course she was incapable of such a locution, and it was silly of him to have thought otherwise even momentarily(用女店员或店员的习语来说，如果她已经说“是”，他会非常失望和受伤。 但她没有这样说！ 她当然不会说这种话，而且他一时也不这么想，要不然真的是太傻了).
谦虚过去时态词经常用在表达陈述(a statement)、提议(a proposal)或建议(a suggestion)的从句中。通常，使用过去时间的概念没有问题。这种用法在下列类型从句中：
I. 用在宾语从句中。例如：
(1) Then I would suggest that you ceased trying to clean your finger.
那么，我建议你停止尝试清洁你的手指。
(2) “Alen , why, are you in love with Stella?”Michael challenged.
“Alen，为什么，你爱上了Stella？” Michael质问道。
“What (is it) made you think I was?”countered Alan, looking alarmed.
“是什么让你认为我是？”Alan反问道，看起来很震惊。
(3) “Suppose we went to one of the Non-Conformist Churches. We can usually count on a good sermon from the minister at Holly Road.”
“建议我们去其中一个不循规蹈矩的教会。(这样)，我们通常可以指望Holly Road的牧师能发表一篇精彩的布道。”
II. 用在it is (high/about) time，it seems之引导的从句中。
A. it is (high/about) time 用法例句(注意：high/about具有强调意味，带有生气或报怨的意味)。
A1. 当我们想表达现在应该做某事，并且行动时间已经有一点晚，使用一般过去式，即应该做某事，但是有点晚。
结构为：It’s (high/about) time + past subjunctive(simple past tense)
例如：
(1) It is time we gave a second thought to Puritanism.
现在是我们重新考虑清教主义的时候了。
(2) It is high time that we decided just what is meant by a word.
正是我们决定一个词的含义的时候。
(3) I’ve felt it coming, you know, and it’s time I really struck out for myself.
我已经感觉到它的到来，你知道的，现在是我真正为自己出击的时候了。
(4) Sidney: Auntie, I know Mother won’t want to be disturbed.
Sidney: Auntie，我知道妈妈不想被打扰。
Miss Fairfield: It’s high time she was.
Fairfield小姐：她早该这样做了。
(5) The censorship is not a branch of military science and study. It is high time that it was made so.
审查制度不是军事科学和研究的一个分支。现在是时候这样做了。
(6) It’s high time you got that car repaired.
你正该把那辆车修一修了。
(7) It’s time you got that car repaired. (This pattern shows a little less urgency.)
你该把那辆车修一修了。(没有使用high，显得不够迫切。)
(8) It’s about time you got that car repaired.
你正该把那辆车修一修了。
(9) It’s high time we bought a new car.
我们正该买一辆新车了。
(10) It’s time we bought a new car.
我们该买一辆新车了
(11) It’s about time we bought a new car.
我们正该买一辆新车了。
(12) It’s high time you went to bed.
你该睡觉了。
(13) It’s time you came to see us. We haven’t met each other for so long.
你应过来和我们碰面。我们很久没有见面了。
(14) It’s time you started thinking about running your own business.
你该考虑经营自己的企业了。
A2. 当我们想表达过去应该做某事，使用过去完成式。
结构为：It was (high/about) time + past perfect subjunctive(past perfect tense)
例如：
It was time you had told him the truth when you had the chance last night.
当你昨晚有机会时，就该告诉他真相。
A3. 但是，当我们认为正点时间已经到达，但是现在仍处于这个正点时间段内，我们可以这样表达，即，应该做某事，为时不晚，例如：
(1) It's time (for you) to go to bed. It’s 10 pm. 你该睡觉了。晚上十点了。
(2) It's time to say goodbye. 该说再见了。
(3) It's time for breakfast. 该吃早餐了。
(4) It’s time to change the rules. 应该改变这条规则。
(5) It’s time to go home. 该回家了。
(6) It’s time to raise your voice. 你该提高声音。
(7) It is time that I give you some idea of my domestic arrangements.
应该让你了解我的家庭安排了。
B. it seems用法例句。
结构为：it seems + preterite (past tense)
(1) It seems as though Oxford and Cambridge might still be permitted to whisper a word in their defense, and that the universities of the provinces were not the impregnable homes of an austere and self-denying erudition.
牛津和剑桥似乎仍然可以为他们的辩护低声说一句话，各省的大学并不是一个朴素而自我否定的学识的牢不可破的家园。
(2) It seems strange that no one noticed that the window was broken.
没有人注意到窗户被打破了，这似乎很奇怪。
不过，it seems也有其用法，这与谦逊过去式没有关系：
seem作为连系动词(copula)，后面接形容词，较少接名词：
(1) It seems strange that no one noticed that the window was broken.
没有人注意到窗户被打破了，这似乎很奇怪。
(2) Glenda seems happier these days.
那些天，Glenda 看起来挺高兴。
我们可以使用非人称结构，it seems或者it seems + that从句/as if从句/as though从句：
(1) It seems that the village shop will have to close down. They can’t find a buyer for it.
村里的商店似乎要关门了。他们找不到买家。
(2) It seems as if he wants everyone to feel sorry for him, but I don’t.
似乎他想让每个人都为他感到难过，但我没有。
(3) It seemed as though time was standing still. She wanted that moment to last forever.
时间似乎静止不动。她希望那一刻永远持续下去。
2.1.1.4 动词过去时态在非现实性语境中的用法(Irrealis)
irrealis(中世纪拉丁语，“非现实性”)，我们现在一般称为虚拟语气(subjunctive mood)，或者假设。动词的过去时态(preterite)常用于表达与事实相对的想法：称为非现实性(irrealis)。这种情况仅发生在从属子句(subordinate clauses)中。前面已经指出，过去时态(past tense)与这种过去时态(preterite)之间除了在“to be”动词的用法上有区别之外，没有正式的区分。在俗语英语中(或者英语口语中)，使用“was”非常流行，下面将引用例子说明。但是，在以过去式或者谦逊过去式态逞现的句子中，不可能使用“was”替换掉“were”。
A. 在带有连接词if、as if、though、as though、等等的条件(condition)、比较(comparison)、和让步(concession)副词从句中。例如：
(1) He makes one realise that if only knew though about the subject, it would abound in both beauty and interest.
他使人意识到，只要知道这个主题，它就会充满美感和趣味。
(2) “Well, what you are thinking is, whether it is fair to him to take me up there in case he is drunk...”
“好吧，你在想的是，如果他喝醉了，带我去那里对他是否公平……”
“If only it was ‘in case’ ”I said. “(Do) You see?”
“前提是‘万一’” 我说道。“你觉得呢？”
(3) I should go and do it now if I were you. Strike while the iron’s hot.
(等价形式：I should go to do it now if I were you. Strike while the iron is hot)
假如我是你，现在我就去做这件事。趁势打铁。
(4) If it were me, I'd go. (I’d go= I should go)
如果是我，我会去。(这是“一种假设的语境”(a hypothetical situation))
(5) If I were you, I would study more/I wouldn't do that/I would go to the doctor/I wouldn't go there.
(6) If only there was something she could do or say to help.
要是她能做些什么或说些什么来帮助我就好了。
(7) Thus, after ten years’ approved service, a teacher might feel assured of a modest competency even though she never attained to headship of school or department.
因此，经过十年的认可服务，即使她从未担任学校或部门的负责人，老师也可能会确信自己的能力适中。
(8) He looks as if he knew the answer.(如果语境显示他看起来知道答案，而事实上他不知道答案，或者他不知道别人认为他知道答案)
他看起来似乎知道答案。
而另一句：
He looks as if he knows the answer.(表示他知道答案)
B. 在主句是“I wish”的宾语从句中。例如：
(1) I wish I liked rice-pudding.
我希望我喜欢米饭布丁。
(2) I wish I were a twin.
我希望我是双胞胎。
2.1.2 祈使句中的谓语动词使用动词根词(动词原形)
2.1.2.1 什么是祈使用句(祈使语气)？
祈使语气(imperative mood)，指表达命令或要求(command)、恳求(entreaty)、建议(advice)、或劝告(exhortation)语义的语气。(注：有的地方将这些归为虚拟语气，但是从区分祈使句和虚拟语气的定义上来讲，理解为祈使句似乎更合理一些)。
2.1.2.2 祈使用句中的动词使用动词原形。
祈使句中的谓语动词只用原形，不受主语人称、数的限制，没有屈折变化，也不与助动词连用。祈使句的这些特征，在与陈述句比较时，只有在主语为第三人称单数，谓语动词为be的情况下时才能明显地体现出来。祈使用句的谓语动词和陈述句、疑问句、虚拟句的谓语动词形式相同。这要从句子结构和所表达的意义去判断。
I. 表示命令的祈使用句，常用的动词有order、command、demand、request、require、ask、urge、prefer、等等。例如：
(1) a. You go and John stay with me. (祈使句——命令语气)
你去，John留在我身边。
b. You go and John stays with me. (陈述句)
(2) (You) be quite. (祈使句——命令语气)
请安静。
You are quite. (陈述句)
你很安静。
(3) (You) Don’t be late. (祈使句——命令语气)
别迟到
You aren’t late. (陈述句)
你没迟到。
(4) You come with me. (祈使句——命令语气)
你跟我来。
(5) You look pale. (陈述句)
你脸色苍白。
(6) Don’t you tell him about that. (祈使句——命令语气)(这儿使用了倒装，自然语序：“You don’t tell him about that”)
你可别把那件事告诉他。
Why don’t you tell him about that? (疑问句)
你干嘛不把那件事告诉他呢？
(7) If you be quiet, I’ll send you away.
如果你安静的话，你可以呆在这儿。(虚拟语气，be在这儿用于推测条件句，是一种比较古老的虚拟语气，在现代英语中可以使用陈述句替代，即：If you are quiet, I’ll send you away)。
(8) It is imperative that the game begin at once. (祈使句)
游泳必须马上开始。
(9) The manager was angry and ordered that this work finish tomorrow. (祈使句——命令语气)
经理很生气，要求明天完成这项工作。
(10) It was ordered that no smoking be allowed in the library. (祈使句——命令语气)
有人下令图书馆禁止吸烟。
(11) The order came that the medical supplies be sent to Beijing for the Sars soon. (祈使句——命令语气)
命令传来，要求尽快将医疗用品运往北京，以应对Sars。
(12) It was required that each student bring enough food for the picnic. (祈使句——命令语气)
要求每个学生带足够的食物去野餐。
(13) It is requested that every student make a plan for the next semester. (祈使句——命令语气)
要求每个学生为下学期做一个计划。
(14) A request is made to the investigation committee that a decision be made as soon as possible. (短语：make a decision (做决定)) (祈使句——命令语气)
要求调查委员会尽快做出决定。
(15) The teacher demanded that the work be finished before 4 o’clock. (祈使句——命令语气)
老师要求作业在4点之前完成。
(16) Their demand is that their wages be increased by 20%. (祈使句——命令语气)
他们要求把工资提高20%。
(17) Tom’s father, as well as his mother, asks he stay in New York for a few days more. (祈使句——命令语气)(这里，从句子成分上来说，这里的“as well as his mother”是状语，起补充说明，虽然在意义上是主语，但是从结构上来看，用逗号隔开了，不是主语，因此这里有干扰，动词ask用一般现在时单数“asks”)
Tom的父亲和母亲都要求他在纽约多待几天。
(18) The management urged that the cost of production be further reduced. (祈使句——命令语气)
管理层敦促进一步降低生产成本。
(19) We prefer that the plan be fully discussed before being put into execution. (祈使句——命令语气)
我们希望这项计划在实施前经过充分讨论。
II. 表示劝告的祈使用句，常用的动词有urge、prefer、等等。例如：
(1) The old worker urged that we use cheaper materials instead. (祈使句——劝告语气)
老工人劝我们改用更便宜的材料。
III.表示建议的祈使用句。
A. 用动词表示的建议
常用的动词有insist、suggest、advise、propose、recommend、等等，这种应该时，我们可以认为其结构为(should)+动词原形，既然是建议，就表示建议人认为“应该”如何如何，只是这个should可以省略；或者直接认为祈使句用动词原形。例如：
(1) The old worker urged that we (should) use cheaper materials instead. (祈使句——劝告语气)
老工人劝我们改用便宜的材料(或，“老工认为我们应该改用便宜的材料”)。
(2) My suggestion is that we (should) send them a message. (宾语从句形式)
我的建议是我们应该给他们捎个口信。
I made a suggestion that we (should) send them a message. (同位语从句形式)
It was my suggestion that we (should) send them a message. (语语从句形式)
(3) The father insisted his daughter (should) be engaged to a rich man.
父亲坚持认为女儿应该和一个有钱人结婚。(父亲强烈的建议)
(4) Mrs. Black insists that she (should) not stay in that old hotel.
Black太太坚持认为她不应该住在那家旧旅馆。(祈使句直接使用not构成否定句)
(5) She made a suggestion that the plan (should) be considered carefully.
她建议存细考虑这个计划。
(6) My suggestion is that she take more exercise, which will do a lot of good to her.
我建议她多锻炼，这样对她有很多好处。
(7)My mom suggests that we (should) eat out for a change this weekend.
我妈妈建议我们周末出去吃饭换换口味。
(8) Jane’s pale face suggested that she was ill, and her parents suggested that she (should) have a medical examination.
Jane苍白的脸表明她病了，她的父母建议她做一次体检。
(9) The doctor’s advice is that the patient (should) not be told about his real physical condition.
医生的建议是不要告诉病人他的真实身体状况。
(10) I think it advisable that he (should) leave for Tokyo soon.
我认为他尽快动身去东京是明智的。
(11) The Reform Club proposed that wages (should) be raised.
改革俱乐部提议提高工资。
(12) Teachers recommend parents (should) not allow their children under 12 to ride bicycles to school for safety.
为了安全起见，老师建议家长不要让12岁以下的孩子骑自行车上学。
(13) His English teacher recommends that he (should) begin a regular degree program.
他的英语老师建议他开始正规的学位课程。
(14) He suggested that we (should) stay for dinner.
他建议我们留下来吃晚饭。
(15) He insisted that I (should) read his letter.
他认为我应该读她的信。
(16) I propose he (should) work full time.
我建议他全职工作。
B. 第二种为在“It is (was)+形容词（或过去分词）+that…”结构中，当形容词是表示愿望、建议、请求、命令、可能、适当、较好、迫切、紧近、重要等词义时，后面的主语从句的谓语用动词原形。例如：
(1) It is necessary that we (should）have a walk now.
我们现在散步是必要的。
(2) It is important that every pupil (should) be able to understand the rule of school.
每个学生都能理解学校的规章制度是很重要的。
(3) It is natural that she (should) do so.
很显然，她应该这么做。
(4) It is essential that these application forms (should) be sent back as early as possible.
这些申请表应尽早地寄回，这是很重要的。
(5) It is vital that enough money (should) be collected to fund the project.
重要的是募集足够的钱，为这个项目提供资金。
(7) It was essential that we (should) sign lease before the end of the month.
我们必须在月底前签租约
(8) It is important that the TOEFL office (should) confirm your registration.
托福办公室确认你的注册是很重要的。
(9) It’s necessary that he (should) have a recognized qualification.
他必须有公认的资格。
(10) It is highly desirable that a new chairman (should) be elected for the committee.
选举一位新的委员会主席是非常可取的。
C. 句子中隐含“想让某人做某事”这种建议的意义。例如：
(1) The idea is that the nation (should) send an unmanned spacecraft to explore the planet first.
他们的想法是，国家应该先派一艘无人驾驶的宇宙飞船去探索这个星球。
(2) There is a general understanding among the members of the Board of Directors that chief attention (should) be given to the undertaking that is expected to bring in highest profit.
董事会成员普遍认为，应主要关注有望带来最高利润的企业。
IV. 表示请求的祈使用句，并且常常在后面加一个附加问句或使用某些客套话。例如：
(1) Mary, bring the glasses in, will you?
玛丽，把玻璃杯拿进来好吗？
(2) (You) go to the theatre,will/won’t you?
去看戏好吗？
(3) (You) see to the baby, can you?
请照看婴孩，好吗？
(4) (You) open the door, will you?
请你把门打开，好吗？