Both 可當 (前置) 限定詞和代名詞用，意為「兩個；兩者；雙方」。
在所有格 + 名詞的前面可以使用 both 或 both of；換言之，both of 跟 all of 和 half of 一樣，of 可以省略。例如：
- Both (of) her parents are doctors. (她的父母親都是醫生)
- Both (of) his sisters are living in Japan. (他的兩個姊姊都住在日本)
Both 可修飾名詞。例如：
- There are five cars on both sides of the road. (路的兩邊各有五輛汽車)
- Both children went. (兩個孩子都去了)
Both 與代名詞連用時，無論代名詞是主格還是受格，both 都位在它們的後面。例如：
- They both need some money. (他們兩人都需要一些錢) (正)
Both they need some money. (誤) - I like them both. (他們兩人我都喜歡) (正)
I like both them. (誤)
但我們可以用 both of + 受格代名詞來當主詞或受詞。例如：
- Both of them (= They both) need some money. (正)
- I like both of them (= them both). (正)
不過，雖然「both of + 受格代名詞」等於「受格代名詞 + both」，但在介系詞後面，通常使用「both of + 受格代名詞」。例如：
- Mary looked at both of us. (瑪麗看著我們兩個) － 優於 Mary looked at us both.。
- This plan is beneficial for both of you. (這項計畫對你們兩人都有利) － 優於 This plan is beneficial for you both.。
Both … and … 與名詞連用時，both 可位在名詞的前面或後面。例如：
- We all like both Tom and Cindy. (湯姆和辛蒂兩個我們都喜歡) (正)
= We all like Tom and Cindy both. (正) - Both Teresa and Amy have pixie cut hairstyle. (泰瑞莎和艾美都留了一頭俏麗短髮) (正)
= Teresa and Amy both have pixie cut hairstyle. (正) - Both men and women like the movie. (男人和女人都喜歡這部電影) (正)
= Men and women both like the movie. (正)
當 both 指的是主詞時，亦即當 both 是主詞的一部份時，它在句中通常位在副詞慣常的中間位置，即主詞和主動詞之間、語氣助動詞或第一個助動詞之後，或當主動詞用的BE 動詞之後。例如：
- We both wanted to live abroad. (我們兩人都想住在國外) － both 位在主詞和主動詞之間。
- They have both been working for that company for five years. (他們兩人都已在那家公司工作了五年) － both 位在語氣助動詞或第一個助動詞之後。
- They were both very generous and friendly. (他們兩人都很大方和友善) (正) － both 位在當主動詞用的BE 動詞之後。
They both were very generous and friendly. (誤) - Who are you like in your family? (你在家中像誰?)
My father I suppose, we’re both quite moody. (我想是像我爸爸，我們兩人都很情緒化) (正) － both 位在當主動詞用的BE 動詞之後。
My father I suppose, we both are quite moody. (誤)
在否定句中，我們不可使用 both，必須改用 either (兩者之中任何一個)。例如：
- John studied chemistry and physics, but he had little interest in either subject. (約翰唸的是化學和物理，但他對這兩門學科都沒有什麼興趣) (正) － little 為否定詞。
John studied chemistry and physics, but he had little interest in both subjects. (誤) - I don’t agree with either of you on these issues. (在這些問題上，你們兩個我都不同意) (正)
I don’t agree with both of you on these issues. (誤) - A: Are Paul and his girlfriend both coming to my birthday party? (A：保羅和他女友會來參加我的生日派對嗎？)
B: I don’t know if either of them are coming. (B：我不知道他們兩人是否會來) (正)
B: I don’t know if both of them are coming. (誤)
必須說明的是，在上句中，either 雖然是個單數字，但在非正式的口說英語中，它通常接複數動詞。不過，在比較正式的情況，either 係接單數動詞，即 … if either of them is coming.。
最後，我們要特別注意 both 這個字所表達的意義；在使用 both 的句子中，動詞所表示的狀態或動作分別及於該兩者中的每一個。所以，
- Both volleyball teams have 20 members.
這個句子的意思是「每支排球隊都有 20 個隊員」，而不是兩支球隊加起來共有 20 個隊員 (亦即每支球隊只有 10 個隊員)。