事實上，as 和 like 幾乎是風馬牛不相及的兩個字，但偏偏卻有不少人把它們當作同義詞，還三不五時將它們互換一下。必須注意的是，as 和 like 只有當連接詞且用作比較時才可互換，此時它們意為「像，好像，就像；如同 (…那樣)，正如 (…那樣)」。誠如大家所知，as 還有幾個很常見的連接詞用法和意思，與 like 更是毫無關聯。
雖然 as 和 like 當連接詞且用作比較時是同義詞，但 like 僅能用於非正式的上下文中，因為迄今傳統的文法書仍將 like 的這項用法視為錯誤。例如：
- Like I said, I enjoy reading novels.
= As I have already said, I enjoy reading novels. (就像我說過的，我喜歡看小說) - Nobody understands her as I do.
= Nobody understands her like I do. (沒有人像我這樣瞭解她) - John got divorced, (just) as his parents had done years before.
= John got divorced, like his parents had done years before. (約翰離婚了，重蹈了多年前他父母婚姻破裂的覆轍) - Like any good grammar books will tell you, cleft sentences are very important structures.
= As any good grammar books will tell you, cleft sentences are very important structures. (正如/就像任何好的文法書會告訴你的一樣，分裂句是非常重要的結構)
As 和 like 除了當連接詞且用作比較時才可互換外，其他用法都不相關。然而，令人遺憾地，還是有人把它們的介系詞用法當作同義詞。As 當介系詞用後面接名詞時意為「以…的身份；作為」，而 like 當介系詞用後面接名詞時意為「像；與…相似，與…近似」，可見兩者的意思完全不同。例如：
- As your father, I’ll help you as much as I can. (身為你的父親，我會竭盡所能幫你)
－ 說這句話的人是聽者的父親。 - Like your father, I’ll help you as much as I can. (就像你的父親，我會竭盡所能幫你)
－ 說這句話的人並非聽者的父親。 - I’ve got a shirt just like that. (我有一件和那件一模一樣的襯衫) (正)
I’ve got a shirt just as that. (誤) - Mary looks like her mother. (瑪麗長得像她媽媽) (正)
Mary looks as her mother. (誤) - The little girl sings like an angel! (那位小女孩的歌聲宛如天使一般！) (正)
The little girl sings as an angel! (誤) - Do you suffer from migraines like me? (你像我一樣患有偏頭痛嗎？) (正)
Do you suffer from migraines as me? (誤) - Like most people, I’d prefer not to live in Taipei. (和大多數人一樣，我寧願不住在台北) (正)
As most people, I’d prefer not to live in Taipei. (誤)
但 As most people would, I’d prefer not to live in Taipei. (正) - Amy works as a waitress. (艾美是個服務生) (正)
Amy works like a waitress. (誤) - She’s worked for a long time as an interpreter in that company. (她長期以來一直在那家公司擔任口譯員) (正)
She’s worked for a long time like an interpreter in that company. (誤)