昨天同事問我一個問題：到底應該說the reason is that還是the reason is because？
比如有的英語老師會很強硬地認為「The reason for the new plan is becausethe situation has changed.」這句話是病句。應該改為：The reason for the new plan isthatthe situation has changed.
有的語法專家也持同樣的觀點，認為the reason is because這種表達是錯誤的，原因有二：
1. Because在這裡多餘了，因為because本來意思就是「for the reason that」，所以the reason is because相當於the reason is for the reason that，意思重複。2.is是系動詞，後面不能跟狀語從句，because引導的是原因狀語從句，所以不能出現在is後面。
但事實上，很多英語作者都會使用「the reason is because」這種表達。
加州大學聖地牙哥分校的語言學學者Gabe Doyle認為，兩種說法都可以。「the reason is because」也是標準英語表達，400多年來都有人這麼用。而且因為reason和because意思上有微弱（mild）的重複就歸為「錯誤」用法有些牽強。
The reason is because is a standard English phrase, one coming from the pen of good writers (Bacon,Frost,Wodehouse) for 400 years. It's grammatically fine, and its supposed redundancy is at worst mild. You're welcome to use the reason is that instead, as both are standard, but there's no good reason to oppose the reason is because.
stackexchange.com是一個英語學習的交流平臺，有人在這個網站上也提出了這個疑問。
排名靠前的兩個回答立場相反，我認為最高票的回答很好地解釋了這個問題。
這兩個句子中：
The reason is because it rained yesterday.The reason is that it rained yesterday.
第二個句子讀起來似乎好一些，因為the reason is because稍微有些重複。
但比較這兩個句子：
The only good reason to go to graduate school in English literature is because you love it.The only good reason to go to graduate school in English literature is that you love it.
相比之下用because更優，因為在reason和because之間有很大的間隙，所以because能更好地點出reason這個主語。
韋氏詞典（Merriam-Webster Dictionary）在一篇名為「The Reason Is Because: Redundant But Acceptable」的文章中明確表態：
沒必要因為「重複」而將其歸為「異類」。因為古往今來這麼寫的人不乏一些赫赫有名的英語大家——Francis Bacon，Jonathan Swift，John Adams等等。如果你覺得the reason is because彆扭，那就不要寫，但不用詬病。
參考連結：
https://motivatedgrammar.wordpress.com/2012/06/28/the-reason-is-because/
https://english.stackexchange.com/questions/34396/is-it-correct-to-say-the-reason-is-because
https://www.merriam-webster.com/words-at-play/usage-of-reason-is-because-redundant