一、句子成分
（一）句子成分的定义：构成句子的各个部分叫做句子成分。句子成分有主要成分和次要成分；主要成分有主语和谓语；次要成分有表语、宾语、定语、状语、补足语和同位语。
（二）主语：主语是一个句子所叙述的主体，一般位于句首。但在there be结构、疑问句（当主语不疑问词时）和倒装句中，主语位于谓语、助动词或情态动词后面。主语可由名词、代词、数词、不定式、动名词、名词化的形容词和主语从句等表示。例如：
During the 1990s, American country music has become more and more popular.（名词）
We often speak English in class.（代词）
One-third of the students in this class are girls.（数词）
To swim in the river is a great pleasure.（不定式）
Smoking does harm to the health.（动名词）
The rich should help the poor.（名词化的形容词）
When we are going to have an English test has not been decided.（主语从句）
It is necessary to master a foreign language.（it作形式主语，真正的主语为后面的不定式）
（三）谓语：谓语说明主语所做的动作或具有的特征和状态。动词在句中作谓语，一般放在主语之后。谓语的构成如下：
1、简单谓语：由一个动词或动词短语构成。如：He practices running every morning.
2、复合谓语：（1）由情态动词或其他助动词加动词原形构成。如：You may keep the book for two weeks. He has caught a bad cold. （2）由系动词加表语构成。如：We are students.
（四）表语：表语用以说明主语的身份、特征和状态，它一般位于系动词（如be, become, get, look, grow, turn, seem等）之后。表语一般由名词、代词、形容词、分词、数词、不定式、动名词、介词短语、副词及表语从句表示。例如：
Our teacher of English is an American.（名词）
Is it yours?（代词）
The weather has turned cold.（形容词）
The speech is exciting.（分词）
Three times seven is twenty one?（数词）
His job is to teach English.（不定式）
His hobby（爱好）is playing football.（动名词）
The machine must be out of order.（介词短语）
Time is up. The class is over.（副词）
The truth is that he has never been abroad.（表语从句）