句子的各个成分之间保持在人称、性、数等方面的一致，这种关系称为一致关系。英语中的一致表现为语法一致、意义一致和毗邻一致三方面。
绝大多数谓语动词在人称和单复数上取决于主语的人称和单复数。如：
The burnt child fears the fire.
Things are invented when the need is great enough.
有时谓语动词的单复数取决于主语的单复数意义，而不是简单地取决于主语的单复数形式，这在集合名词作主语时尤其如此：当主语强调整体时，谓语动词用单数；当主语强调构成集合的各个成员时，谓语动词用复数。如：
The basketball team consists of 20 players.（指整个球队）
The basketball team are having a bath now.（指篮球队的队员）
当主语是由连词等连接的一个短语时，往往采取就近原则，即谓语动词的单复数形式取决于最靠近它的名词或代词的单复数形式和意义。如：
Either the sweater or the shirts were a good buy.
Either the shirts or the sweater was a good buy.
1.谓语动词根据主语意义及就近原则而定的情形：
⑴单复数形式相同的名词用作主语时，要根据它们所含的数量概念来决定谓语动词的单复数形式。如：
A sheep is running along the river.
Some sheep are running along the river.
常见的这些名词有：aircraft， fish， means， sheep， species， works， Chinese， Japanese， swine等。
⑵可数的集体名词，如果作为一个集合概念来看，它表示单数意义，就应该遵循语法一致的原则，动词用单数形式；如果强调的是个体，它表示的就是复数意义，动词用复数形式。
如：
The audience was enormous.
The audience were greatly moved at the word.
常见的这些名词有：army，audience，class，club，jury，public，school，staff，government，team等。
⑶当数学运算中的数词作主语时，谓语动词用单复数均可，但若用了plus， minus，
multiplied或divide时，谓语动词多用equals.
Two fours are eight.
6 multiplied by 3 equals 18.
Four from five leaves one.
⑷在强调句型“It is/was…that/who…”中，强调主语时，that/who引导的从句的谓语动词的形式取决于被强调词的单复数形式或其意义。
It is precisely the people who create history.
⑸“the minority/majority of + 名词”短语作主语时，谓语动词的单复数形式取决于名词的单复数形式。如：
The majority of students were on Ben‘s side.
⑹“all （any， some， a lot， lots， the rest， none， loads， the reminder和分数名词短语）of + 名词“作主语时，若名词为复数意义，谓语动词用复数形式；否则用单数形式。
Half of them are here.
All the land is cultivated.
Tree fourths of the surface of the earth is sea.
⑺“…form（s） / kind（s） / type（s） of + 名词”作主语时，谓语动词的单复数与form（s）等的单复数一致，此时，若名词是不可数名词，谓语动词也要用复数形式。如：
This kind of book sells well.
Two kinds of salt have been proved to be harmful to human body.
⑻“plenty （part， half， rest等） + 名词”作主语时，谓语动词与of后面的名词的单复数形式一致。如：
Half of the guests were here.
⑼由并列连词（or， either…or， neither…nor， not only…but （also）等）连接的并列成份作主语时，谓语动词按就近原则与其保持一致。如：
Neither you nor I am right.
Either Jack or his sisters are going to the cinema.
⑽在“here， there”引导的结构中，如果有多于一个的主语，谓语动词与邻近的主语取得一致。如：
There are two books， a rule and a pen on the desk.
Here is a table， some chairs， and a few desks in the room.
⑾“the + 形容词或分词”作主语时，若指一个人或抽象概念，谓语动词用单数形式；若指一类人，谓语动词用复数形式。如：
The deceased was his mother.
The good are demanding their ringhts.
⑿由as well as， as much as， no less than， rather than等连接的并列主语，在意义上更强调第一主语。根据语法一致的原则，动词形式通常取决于第一主语的数和人称。如：
I， as well as him， am ready for outing.
He as much as us is responsible for it.
2.谓语动词用单数形式的情形
⑴不定式短语、动名词及名词从句作主语时，谓语动词用单数形式。如：
To become doctors is their ambition.
Reading without comprehension is no good.
What that country needs is more jobs and lower taxes.
⑵表示时间、距离、重量、长度、价值等的名词，不论单复数，当作主语时，谓语动词均用单数形式。如：
Twenty years is a long period of his life.
Five thousand dollars is more than I can afford.
⑶用and连接的名词或代词前有every， each， no， many a等修饰时，谓语动词用单数。如：
Every one of the figures was checked at least twice.
⑷事件、国名、机构名称、书籍及其它作品的名称作主语时，谓语动词均用单数形式。
The United Nations was formed in 1945.
Great Expectation is a very famous novel.