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 whom are clever. 他有两个儿子，都很聪明。

He has three sons, all of whom are clever. 他有三个儿子，都很聪明。

He has two sons, either of whom is clever. 他有两个儿子，哪个都很聪明。

He has three sons, any of whom is clever. 他有三个儿子，哪个都很聪明。

He has two sons, neither of whom is clever. 他有两个儿子，两个都不聪明。

He has three sons, none of whom are clever. 他有三个儿子，个个都不聪明。

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 is interesting. 两个故事都没有趣。

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。