ever
ever 和 never 表達的是過去一個不明確時間的概念（例如：Have you ever visited Berlin?）ever 和 never 一律放在主要動詞（過去分詞）前。ever 是用在：
問句中
舉例
Have you ever been to England?
Has she ever met the Prime Minister?
在否定句
舉例
Haven't they ever been to Europe?
Haven't you ever eaten Chinese food?
用 nothing + ever 或 nobody + ever 形式的否定句
舉例
Nobody has ever said that to me before.
Nothing like this has ever happened to us.
帶有「the first time」的句子
舉例
It's the first time that I've ever eaten snails.
This is the first time I've ever been to England.
never
「never」意指「過去一次也沒有」，跟「not ..... ever」的意思是一樣的。（例如：I have never visited Berlin.）
I haven't never been to Italy.
I have never been to Italy.
already
「already」意指某個動作已經發生在過去一個不明確的時間，傳達「無需再重複」的意思。
舉例
I've already drunk three coffees this morning. (= 而且你還又給我一杯！）
Don't write to John, I've already done it.
這個字也會用在問句中：
Has she finished her homework already?
「already」可以放在主要動詞（過去分詞）前，或放在句尾：
I have been to Tokyo already.
yet
「yet」用於否定句和問句，一般會放在句尾；意指在過去和現在的一段時間內曾經有（或從未），直到現在曾有（或未曾），以及包括現在有（或沒有）。
舉例
Have you met Judy yet?
I haven't visited the Tate Gallery yet
Has he arrived yet?
They haven't eaten yet