Half 意為「半，一半」，如 half an hour (半小時)，half a watermelon (半個西瓜)。Half 的複數為 halves。例如：
- I cut the cake into (two) halves.
= I cut the cake in half. (我把蛋糕切成兩半)
Half 可用作前置限定詞 (predeterminer)、名詞、形容詞和副詞。Half 最常見的句型是「half of + 受詞」，這裡的受詞為代名詞或特指的名詞 (所謂特指的名詞，就是名詞的前面加上 the, that, this, these, those 或所有格，如 my, John’s 等等)。在此句型中，half 是當名詞用。由於 half of 跟 all of 和 both of 一樣，of 可以省略，當 of 省略時，half 就變成了前置限定詞。例如：
- Roughly half (of) the students in my class could not identify Oman, an Arab country, on a map of the world. (我班上約有半數的學生無法在世界地圖上找到阿拉伯國家阿曼的位置)
- Tom spends half (of) his salary within four or five days of receiving it. (湯姆在領到薪水後的四、五天內就花掉了一半)
- At least half (of) those children are not afraid of the dark. (那些小孩至少有半數不怕黑)
若 half of 後接受格代名詞，則 of 不可省略。例如：
- Almost half of us did not agree that Peter should be invited. (我們有將近一半的人都不同意邀請彼得) (正)
- Almost half us did not agree that Peter should be invited. (誤)
若 half of 後接計量單位，則不可使用 of，如上面所舉的 half an hour (半小時)。例如：
- We had to wait half an hour for a train. (我們必須等半小時才有火車) (正)
We had to wait a half hour for a train. (正)
－ 在美式英語中，a half hour (或其他計量單位) 的說法或寫法比 half an hour 來得常見。
We had to wait half of an hour for a train. (誤)
We had to wait half hour for a train. (誤) - It’s approximately half a kilometer to that university. (距離那所大學約半公里) (正)
It’s approximately a half kilometer to that university. (正)
It’s approximately half of a kilometer to that university. (誤)
It’s approximately half kilometer to that university. (誤) - She bought half a dozen eggs yesterday. (她昨天買了半打雞蛋) (正)
She bought a half dozen eggs yesterday. (正)
She bought half of a dozen eggs yesterday. (誤)
She bought half dozen eggs yesterday. (誤)
這裡還有一篇有關 Half 的用法說明，歡迎參閱。