形容词和副词比较等级用于句子当中便形成比较结构（comparative construction）。英文比较结构最主要的有三种：as … as结构，more … than结构和the most结构。当然，也要考虑某些限定词和代词的比较等级构成的比较结构。

1. as … as结构

这种结构的基本模式是：as+形容词或副词原级+as-分词

This car runs as fast as that one.

否定形式：

This car does not run as fast as that one.

This car runs less fast as that one.

带有as … as 结构的句子也可能主语相同，而比较项目不同。

He is not as wise as he is witty.

也有可能两个主语和两个比较项目都不同。

This swimming pool is not twice as wide as that one is long.

当然as … as结构还有变体形式——as+形容词原级+名词词组+as-分句。

George is as efficient a worker as Jack.

2. more … than结构

这种结构我们见得也多，也就是形容词或副词比较级+than-分句。

John is brighter than Bob.

否定形式：

This parcel is less heavy than that one.

This parcel is not so/as heavy as that one.

3. (the)+形容词/副词最高级+比较范围

如果是三个或三个以上的人或物进行比较，就要使用形容词和副词的最高级。

The Sahara is the biggest desert in the world.

This is the most interesting book I have ever read.