代词一般用来指代一个事物，但这个事物有时候是个个体事物，有时候是个群体事物，所以代词也有单复数的区别。

比如我们学的人称代词：我工作~我们we、你you~你们you、它it~它们they，就是单复数的区别。代词和物主限定词单、复数形式的选择通常取决于它们的指示对象，即先行项的单、复数形式。例，All members of the group have already made their decisions. 这里，all members是指示对象(先行项)，所以其后的代词选用their。关于代词单、复数形式的选择，还需要注意以下几点：

1. 先行项为every-，some-等复合词时：语法一致原则，代词一般用单数：Anybody can come here if he is interested.当先行项为everybody，everyone时，代词一般用复数更为自然。Everyone was clapping their hands.当先行项为everything，anything，something，nothing时，代词用单数。Everything in the bag is broken, isn’t it?

2. 先行项为并列结构时：意义一致原则。My friend and roommate has done well in her exam, so she is happy now.My friend and roommate have agreed to lend their bikes to me.

3. 先行项为集体名词时：意义一致原则。The team has won its first game.The team are now preparing themselves for the next game.

3. 先行项为“...+each”时：若each在动词后，代词则为单数：They had each his own problem.若each在动词前，代词则为复数：They each had their problems.