不好意思
剛剛 google 一下
找到一個類似的問題
結果回答也是不能用 would
有點被搞混中 @@
網址
http://www.englishforums.com/English/ConditionalWithModalVerbs/mghl/post.htm
節錄如下
Why is #1 correct and #2 is incorrect?
1. If she has time, she could go to the party.
2. If she has time, she would go to the party.
Strictly speaking, the modals are not tensed. However, they developed
historically from tensed verbs. Each group below shows a "historical present
/ past" pair.
can / could
shall / should
will / would
may / might
must - not paired
In modern English, any of these can be used in a single clause sentence, but
when it occurs in just one of two or more clauses in the same sentence, it
needs to be matched correctly with the tense in the other clause.
Typically, when the accompanying clause is an "if" clause, the historical
present tense forms go with present tense verbs, and historical past tense
forms go with past tense verbs. However, "could" and "might", meaning "may"
("it is possible"), can be used with present tense verbs (as well as with
past tense verbs). "should" has lost most of its force as a past tense and is
better thought of as a present tense form in modern English, meaning "it is
advisable". ("shall" is the least used of the modals shown above.) The result
of all these historical changes is that in modern English we have far more
choices in sentences with a present point of view than in those with a past
point of view.
With this in mind we have:
If she has [present] time, she [can, could, (shall), should, will, may,
might, must] go to the party. [not "would']
If she had [past] time, she [could, would, might] go to the party. [not
"should"]
※ 引述《CK100 (cJ)》之銘言：
: 首先would是假設語氣
: 而if也是假設語氣，
: 所以在主要子句跟從屬子句都需要有假設的語氣
: 既然在從屬子句中已經使用了if做為開頭的連接副詞帶有假設語氣
: ，那麼if+S+V+O中V不需要有重複的假設語氣，故用肯定即可。
: 再者，在主要子句中必須存有假設語氣，所以使用假設語氣的助動詞。
: I would talk to my brother if I have a problem. 是正確的
: 所以這種假設語氣不用死背，要靠理解。
: 主要子句(假設語氣)+從屬子句(假設語氣)
: 假設語氣助動詞有:
: can could
: may might
: should
: will would
: could, would, might 都是指比較輕微的可能性
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