while 不是也可當連接詞 表 當 的意思?

在當「連接詞」用時，when和while所帶出的副詞子句提供的狀況不同：通常when表示特定的時間，while表示期間，但有時when子句也有進行式，但when的副詞子句提供的是「未來的」時間座標時，只能用「現在簡單式」或「現在完成式」。

Trade began between Europe and the Far East.所表示的是一個過去的起點，不是過程，所以不能用表示「在那段期間」的連接詞while。也就是說其動詞begin是𣊬間動詞，在發生的當下就結束了，不用進行式。但可以用表示「在那時」的when。

when interroga. adv=at what time; on what occasion;
relative adv:-eg:-with day, time,,etc as antecedent at or on which
eg:-It was in 1600 when tea was introduced.(rel. adv)
Hence :-eg:-Tea was introduced to Europe in the early 1600s, (when) trade began between Europe and the Far East.
while conjunction;eg:-Trade began while Tea was introduced to Europe.

when 更合適
while
conjunction
: during the time that

—used to make a statement that describes how two people, groups, etc., are different

: in spite of the fact that
Full Definition of WHILE

1
a : during the time that <take a nap while I'm out>
b : as long as <while there's life there's hope>
2
a : when on the other hand : whereas <easy for an expert, while it is dangerous for a novice>
b : in spite of the fact that : although <while respected, he is not liked>
3
: similarly and at the same time that <while the book will be welcomed by scholars, it will make an immediate appeal to the general reader — British Book News>