形容詞 alternate 意為「(兩個) 交替的，輪流的」，通常用於名詞前；副詞 alternately 意為「(兩個) 交替地，輪流地」。若指時間，它們則分別意為「間隔的」和「間隔地」，與 every other day (隔天)、every other week (隔週) 等片語同義。例如：
- There have been a couple of weeks of alternate sunshine and rain recently. (最近幾個禮拜都是時晴時雨)
- Mary and John saw each other on alternate Sundays. (瑪麗和約翰每隔一個星期天相會一次)
= Mary and John saw each other every other Sunday. - The teacher criticizes and praises Peter alternately. (老師對彼得時而讚揚，時而批評)
- Tom was alternately pleased and angry. (湯姆時而高興，時而生氣)
形容詞 alternative 意為「可供替代的；可供選擇的」，僅用於名詞前；副詞 alternatively 意為「(用來建議其他可能性) 或者；要不」。例如：
- They’re seeking an alternative venue for the concert. (他們正在尋找其他可舉辦演唱會的場地)
- We are now looking for an alternative method. (我們正在找一個可以替代的辦法)
- Or alternatively we could eat out. (要不，我們也可以到外頭吃飯)
從上述可知，alternate(ly) 和 alternative(ly) 儘管拼字相近，但意思截然不同。因此，我們不能用 alternative(ly) 來替代 alternate(ly)。例如：
- I go and visit my grandparents on my mother’s side on alternate days. (我每隔一天去探視我外祖父母一次) (正)
- I go and visit my grandparents on my mother’s side on alternative days. (誤)
同樣地，alternate 也不可用來替代 alternative。然而，這僅適用於英式英語，因為美式英語也使用 alternate 來表示 alternative「可供替代的；可供選擇的」意思。例如：
- The government has so far failed to set out an alternative plan. (政府迄今還未提出替代方案) (正)
- The government has so far failed to set out an alternate plan. (誤 － 英式英語)
- The government has so far failed to set out an alternate plan. (正 － 美式英語)
不過，無論是英式英語或美式英語，alternately 都不可用來替代 alternatively。例如：
- We could drive all the way. Alternatively, we could fly. (我們可以一路開車，或者搭乘飛機) (正)
- We could drive all the way. Alternately, we could fly. (誤)