1. 这三个词都用来谈论两者：both 意为“(两者)都”，either意为“(两者中)任意一个”，neither 意为“(两者)都不”。若要指三者或三者以上，分别用 all 意为“(三者)都”，any 意为“(三者中)任何一个”，none 意为“(三者)都不”等。比较：

He has two sons; both of them are clever.

He has three sons; all of them are clever.

He has two sons; either of them is clever.

He has three sons; any of them is clever.

He has two sons; neither of them is clever.

He has three sons; none of them are clever.

2. 它们既可用作代词，也可用作形容词。用作形容词时，both 后接复数名词，而 either 和 neither 之后要接单数可数名词。如：

Both of the brothers are here. / Both brothers are here. 兄弟俩都在这儿。

Either of the books will do. / Either book will do. 两本书中哪一本都行。

Neither of the stories is interesting. /Neither story isinteresting. 两个故事都没有趣。

【注】代词 both, either, neither 用作主语时，both 之后的谓语动词总是复数，either 和 neither 后的谓语动词通常用单数。

3. 这三个词都可用作连词，但搭配和意义各不相同。总的说来，要注意它们应连接两个平行对等的句子成分(即同为两个主语、谓语、宾语、状语等)：

(1) both……and……表示两者兼有。如：

She was both tired and hungry. 她又累又饿。

He speaks both English and French. 他既说英语又说法语。

(2) either……or……表示两者或两种可能性中任择其一。如：

He must be either mad or drunk. 他不是疯了就是醉了。

You can either write or phone to request a copy. 你可以写信可打电话来索取一本。

(3) neither……nor……表示两者都否定。如：

It’s neither cold nor hot. 天气既不冷也不热。

He neither knows or cares what happened. 他对所发生的事既不知道也不关心。

【注】以上连词连接主语时，both……and……一般只与复数谓语连用，either……or……和 neither……nor……则通常根据就近原则，要求谓语动词与最邻近主语的人称、数保持一致。如：

Either you or I am wrong. 不是你错就是我错。

Neither he nor she was at home. 他和她都不在家。

3. 注意下面两个同义句：

两边都有商店。

正：There are shops on both sides.

正：There are shops on either side.

两个我都不要。

正：I want neither of them.

正：I don’t want either of them.