S是个简单的英文字母，可以加在可数复数名词后面，也可以用在简单现在时态动词的后面，以表示主语是单数第三人称。例如：

① He walks to school every day.
② Mary gets up early every morning.
③ That woman often talks loudly.

除了把单数名词变成复数名词以及表示单数第三人称之外，“s ”还出现在某些单字上，使它和没有“s”的字呈现出两个不同语义：“beside”和“besides”便是个好例子。

“Beside”是“在……旁边”的意思：“besides”是“除此之外”的意思。两者都是介词，但后者也是个副词。有些人把这两个字等同起来，互相对换，这是大错特错的；因此，④和⑤不对，要改为 ⑥和⑦。

④ Susan is sitting besides me.
⑤ Beside dancing, the children also sang.
⑥ Susan is sitting beside me.
⑦ Besides dancing, the children also sang.

一般上说，“beside”在句子后半部出现，如：

⑧ Some people prefer living beside the sea.
⑨ The small boy is standing beside his mother.

“Besides”的位置不一；可以在句前，也可在句尾，如：

⑩ Besides being a diligent student, Peter is also a good athlete.
11. I have written some other books on language learning besides this one.

上述两个例子中的“besides”是介词；它也可以当副词，如：

12. I like reading; besides, I also like writing.
13. He sings pop songs. Besides, he also listens to classical music.

注意：当副词的“besides”要用句号（.）或分号（;）隔开。

为了使句子多样化，12和13两个句子可以联合起来变成一个较长的句子，但意思不变。因此，例12可以连接成⑿（a）-（e）；例13也可以重新构成⒀（a）-（e）.

⑿（a） I like reading and writing.
（b） I like reading as well as writing.
（c） I like both reading and writing.
（d） I like not only reading but also writing.
（e） Besides reading, I also like writing.

⒀（a） He sings pop songs and listens to classical music.
（b） He sings pop songs as well as listening to classical music.
（c） He not only sings pop songs but also listens to classical music.
（d） Besides singing pop songs, he also listens to classical music.
（e） He listens to classical music in addition to singing pop songs.