S是個簡單的英文字母，可以加在可數復數名詞后面，也可以用在簡單現在時態動詞的后面，以表示主語是單數第三人稱。例如：

① He walks to school every day.

② Mary gets up early every morning.

③ That woman often talks loudly.

除了把單數名詞變成復數名詞以及表示單數第三人稱之外，“s ”還出現在某些單字上，使它和沒有“s”的字呈現出兩個不同語義：“beside”和“besides”便是個好例子。

“Beside”是“在……旁邊”的意思：“besides”是“除此之外”的意思。兩者都是介詞，但后者也是個副詞。有些人把這兩個字等同起來，互相對換，這是大錯特錯的;因此，④和⑤不對，要改為 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.

一般上說，“beside”在句子后半部出現，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.

上述兩個例子中的“besides”是介詞;它也可以當副詞，如：

12. I like reading; besides, I also like writing.

13. He sings pop songs. Besides, he also listens to classical music.

注意：當副詞的“besides”要用句號(.)或分號(;)隔開。

為了使句子多樣化，12和13兩個句子可以聯合起來變成一個較長的句子，但意思不變。因此，例12可以連接成⑿(a)-(e);例13也可以重新構成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.