請問為什麼會有 「If 現在式, 過去式」 這種句型
發現當搭配 If you want ..., sth would be 的時候，特別容易出現
雖然也有 「If 過去式, 過去式」 這樣的用法，還是說這是特例，兩者皆可？

假設語態，不外乎、但也只有以下幾種，在各大文法書都可以查到：
^^^^
If 現在, 現在 (一般的常理，是一種恆古不變的概念)
→ If a girl says no, she means yes.

If 過去, 過去 (過去的常理，但現在未必還是一樣)
→ If he was here, he used to help everyone.

If 現在, 未來 (單純假設，指未來會發生)
→ If he is here, he will help you. (只要有他，就能得到幫助)

If 過去, 過去助動詞+V (與現在不符，但若條件可以成立，可能會發生)
→ If he were here, he would help you. (現在人不在)

If 過去完成, 過去完成 (與過去不符，但若過去曾經滿足條件，過去當時就會發生)
→ If he had been here, he would have helped you. (當時人不在)

If S should V, 助動詞 + V (萬一如何)
→ If he should be here, he would help you. (雖然會help you，但要看他的心情)
→ If he should be here, he will help you. (沒意外都會help you)

針對單純假設的情況，參考賴世雄的文法書說道：
「我們已知純條件假設語氣的主要子句中，助動詞均用現在式，但should為唯一例外。」
也就是說 would 並沒有包含在內，為何會出現以下句子？
文法上有沒有問題？是否這些都屬口語，非正式用法？

※句型： If you want ..., sth would be *-est ... 還蠻常出現的

If you want to rotate an object, which tool would be most helpful?

If you want to connect with the world, English would be your best choice.

Which branch of the military would be best if you want to become
a physical therapist?



下面兩句基本上是一樣出處，要表達的意義也應相同，
但是1978年寫的是 「If 過去式, 過去式」
1980年的卻是 「If 現在式, 過去式」
Writing for a penny a word is ridiculous. If a man really wanted
to make a million dollars, the best way to do it would be start
his own religion.
- Los Angeles Times (27 August 1978)

Writing for a penny a word is ridiculous. If a man really wants
to make a million dollars, the best way would be to start
his own religion.
- "Scientology: Anatomy of a Frightening Cult"
by Eugene H. Methvin. Reader's Digest (May 1980)



下面例句，從對話二、三句判斷，go back to Manchester 應該還沒發生
也就是說 "she" 有意圖、即將在 "tonight" go back
所以這應該是「未來假設」：如條件達成，就會發生變成事實
為何不用 it will be best if I go back ...

"Perhaps it would be best if I went back to Manchester tonight," She said.
"If you want to."
"I don't want to, Joe. I just think it would be best."
- A Death Divided by Clare Francis (2011)

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