英語(yǔ)中有三個(gè)不定代詞，它們只用于兩者，不用于表示三者。這三個(gè)不定代詞是 both, either, neither。這三個(gè)不定代詞在中考英語(yǔ)考題中經(jīng)常被考查到，且很容易出錯(cuò)，所以同學(xué)們應(yīng)引起高度注意。

both, either, neither 這三個(gè)不定代詞都用來(lái)談?wù)搩烧?，其中both 意為“(兩者)都”， either意為“(兩者中)任意一個(gè)”，neither 意為“(兩者)都不”。若要指三者或三者以上，分別用 all 意為“(三者)都”，any 意為“(三者中)任何一個(gè)”，none 意為“(三者)都不”等。比較：

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.

這三個(gè)表示“兩者”的不定代詞除用作代詞，還可用作形容詞。注意，用作形容詞時(shí)，both 后接復(fù)數(shù)名詞，而 either 和 neither 之后要接單數(shù)可數(shù)名詞。如：

Both of the brothers are here. / Both brothers are here. 兄弟倆都在這兒。

Either of the books will do. / Either book will do. 兩本書(shū)中哪一本都行。

Neither of the stories is interesting. / Neither story is interesting. 兩個(gè)故事都沒(méi)有趣。

注：不定代詞 both, either, neither 用作主語(yǔ)時(shí)，both 之后的謂語(yǔ)動(dòng)詞總是復(fù)數(shù)，either 和 neither 后的謂語(yǔ)動(dòng)詞通常用單數(shù)。