概念：冠词是置于名词前并限定名词意义的虚词。英语中的冠词只有定冠词和不定冠词两种，其中定冠词只有the这一种形式，不定冠词只有a和an这两种形式。名词前若不用冠词时，又称作零冠词。不定冠词之所以冠以“不定”两字，就是因为它的主要特点就是“不确定”或“泛指”；定冠词之所以冠以“定”字，就是因为它的主要特点是“确指”或“特指”。
1a 与 an 的用法区别
1.基本区别：原则上说，a用于辅音前；an用于元音前。辅音前用a的例子如: a book, a student, a school, a house, a magazine 等；元音前用an的例子如: an egg, an apple, an object, an idea, an ugly thing 等。
2.易错说明：hour, honest, honor 等单词的拼写虽然以辅音字母h开头，但其读音却以元音开头，因此，前面要用an。反过来，有些单词虽然以元音字母开头，但其读音却以辅音开头，那么它们的前面应用a而不是an，这些词常见的有useful, university, usual, European, united, one-eyed, one-way 等。
此外，对于数字、字母以及由单词首字母构成的缩略词，其前到底是用a还是an，也需根据读音来确定，如下：
He has an 11-year-old daughter.
Our daughter sent us an SOS for some more money.
2冠词在句中的位置
1. 通常位置：一般说来冠词放在单数可数名词之前(如 a man / the man)，如果名词有其他定语，不定冠词应放在定语之前(如a good man / the good man)。
2. 特殊位置：在下面情况中，冠词的位置比较特殊，需要注意。
① 单数可数名词被 such, many, half, what 等修饰时，不定冠词应置于其后，这个大家看例子就很容易明白，而且平时基本不会出错。
He arrived half an hour ago.
He couldn’t afford to pay such a price.
② 单数可数名词前作定语的形容词被 as, so, how, too 修饰时，通常采用 “as / so / how / too + 形容词 + a / an + 名词”这样的词序。
He didn’t know how great a mistake he had made.
It is too difficult a job for me to finish in so short a time.
③ 当定冠词与 all, both, half 表倍数的 double, twice, three times 等分数词等一起修饰名词时，定冠词应放在它们之后。
Turn off all the lights before you go to bed.
Everything was almost double the normal price.
3不定冠词的基本用法
1. 表类别：即指人或事物的类别。
A teacher is a person who teaches.
2. 表数量：即表示数量“一”。
I’ll be able to finish it in a day or two.
3. 表同一性：即表示“同一”，说明事物的同一性质、特征、大小或程度等。
This hat and that one are of a shape.
4. 表程度：用于most前表示“非常”“十分”。
It’s a most boring book.
4不定冠词的考点性用法
1. 用于序数词前：表示“再一”、“又一”。
She thanked him a second time.
Shall I ask her a third time?
2. 用于由动词转化来的名词前：表示一次、一番等义(通常与 have, take, make, give 等动词连用)。
We’ve already had a try at it.
I went down to the beach and took a swim.
3. 用于专有名词前：相当于a certain，意为“一个”“某个”。
The house next door has been bought by a Mr Jones.
4. 用于抽象名词前：使之具体化，表示与该之相关的具体的人或事。
He was a success in business.
It’s a pleasure to talk with you.
5定冠词的基本用法
1. 表示特指：特指某(些)人或某(些)物(包括用于上文提到过的人或物之前，以及说话双方都知道的人或物)。
We have a cat and two dogs. The cat is black and the dogs are white.
2. 表示独一无二：用在世界上“独一无二”的事物的名词前。
The earth goes round the sun.
He looked up at the stars in the sky.
3. 用于最高级前：即用于形容词或副词的最高级前。
Who picked the most apples?
Of the four of us, I sang the worst.
4. 用于序数词或方位词之前。
He was the first man to think of it.
Italy is in the south of Europe.
5. 用于乐器名词前：表示相应乐器的演奏。
Besides the violin, he plays the piano and the flute.
6. 表示人体部位：用于某些介词短语中指身体的某个部位。
He patted me on the back.
We caught him by the arm.
7. 用于表示一家人：用于在姓氏的复数形式之前表示一家人或夫妇二人。
The Smiths live in the apartment above ours.
8. 用于江河湖海等前：用于江河湖海、山脉群岛、海湾海峡等地理名词前。如：
The Yellow River flows into the Yellow Sea.
9. 用于某些含有普通名词的专有名词前：用于某些国名、组织机构、建筑物、报纸杂志、会议条约等含有普通名词与其他词构成的专有名词。
We visited the Great Wall yesterday.
6定冠词的考点性用法
1. 用于整十的复数数词前：表示几十年代。
This happened in the seventies.
2. 用于比较级前：用于“the+比较级，the+比较级”结构中表示“越……就越……”。
The sooner we operate now the safer.
The better I knew him, the more I liked him.
3. 用于表示类别：用于“the+某些形容词或过去分词”中表示一类人。
Do you think the rich should pay more taxes to help the poor?
The sick and the wounded were sent home.
4. 用于国籍名词前表总称：用于“the+某些国籍的形容词”中表示某国人的总称。
The French are famous for their food.
The British drink a great deal of tea.
5. 用于集合名词前表总称：用于“the + police / public等集合名词”中表示这类人的总称。
The police are looking for the murderer.
6. 用于修饰same, only, very等形容词：即用于“the same / only / very +名词”结构中。
That’s the only reason.
Do you belong to the same class?
My view is the very opposite of his.
7. 用于单位名词前表示标准：即用于“单位词”（hour, day, month, year, dozen, gallon, ton, yard等）前表示标准，相当于汉语的“按”“论”“每”等。
They let out cars by the day.
Do you sell eggs by the kilo or by the dozen?
但是，by weight（按重量）习惯上不用冠词。
Bananas are usually sold by weight.
7使用零冠词的典型情形
所谓用零冠词，即既不用定冠词，也不用不定冠词。这类情况主要有：
1. 表泛指的不可数名词或复数名词前。
Snow was failing.
Children get a better education today than at any time in the past.
2. 倒装的让步状语从句中：在as(虽然)引导让步状语从句前面的单数可数名词前不用冠词。
Child as he was, he knew how to help others.
3. 某些特殊词前：例如在man(人，人类), word(消息)的前面不用冠词。
Man is a rational animal.
Word came that he had married again.
又如动词 turn(变成)，go(变成)后作表语的名词前通常用不用冠词。
He was a teacher before he turned writer.
4. 独立主格结构中：在表示伴随或补充说明用用的独立主格结构中，名词前不用冠词。
The teacher came in, book in hand.
He was sitting in the chair, pipe in mouth.
5. “(a) kind [sort] of＋名词”结构的“名词”前：该结构中的“名词”不管是单数还是复数，其前都通常用零冠词。
This kind of book is very interesting.
He is the sort of person I really dislike.
6. 表抽象意义的单数名词前：当单数可数名词含义抽象化具有形容词意味时，通常用零冠词。
I was fool enough to accept his offer.
Are you man enough for this dangerous job?