Before 可當介系詞、副詞和連接詞用。在進入主題之前，必須再次強調一點：在寫作中，我們經常會用到 as mentioned above (如上所述，如上面所提及的)、as noted above (如上面所指出的)、as demonstrated above (如上所示)、as shown above (如上所示) 和 as stated above (如上所述，如前所述) 等片語來表示上文、上面或之前所提到的事物，但在這些片語中，不可使用 before 來代替 above。例如：
- As stated above, there is no shortcut for learning English grammar. (如上所述，學習英文文法沒有捷徑) (正)
As stated before, there is no shortcut for learning English grammar. (誤) - As noted above, the government lacks efficiency. (如上面所指出的，這個政府缺乏效率) (正)
As noted before, the government lacks efficiency. (誤)
Before 用作介系詞時意為「在…之前 (earlier than)；在…前面 (in front of)」，其後最常接名詞片語來表示在 (某個時間點、事件或行動) 之前、在 (某地點) 前面、在 (某人或某物) 面前、(在列表或一系列物件中) 在…之前。例如：
- I regularly go for a run before breakfast. (我經常在早餐前跑步)
- She got there before me. (她比我先到那裡)
- Turn right about a kilometer before the railway station. (在火車站前約一公里處右轉)
- A few miles before the border the refugees were stopped at an army checkpoint. (難民在距離邊界數英里的一個軍事檢查哨被攔了下來)
- Before the library stood a bronze statue of Chiang Kai-shek. (圖書館前矗立一尊蔣介石銅像)
- John stood up before all his colleagues and asked Mary to marry him. (約翰在所有同事面前站起來向瑪麗求婚)
- The letter U comes before V in the English alphabet. (在英文字母表中，U 排在 V 前面)
- His name comes before mine on the list. (名單上他的名字排在我的前面)