這幾個連詞用虛擬語氣的較為普遍,但也要看具體情況.
1、 有時候表示事實相符的真實語氣,如：
We shall go provided that the weather is fine 只要天晴, 我們就去.
Suppose he can't come, who will do the work? 如果他不能前來, 誰來做這項工作呢?
I will lend you the book on condition that you return it on Monday. 如果說你能在星期一還我,我可以借給你這本書.
2、多數(shù)情況下表示與事實相反的虛擬語氣,如：
Provided it was fine we would have a pleasant holiday. 如果天氣好, 我們的假日真的有可能過得非常愉快（但是事實不是如此）.
Supposing your father saw you now, what would you say?退一步說你父親現(xiàn)在看到了你, 你該怎么說?
I will go abroad on condition that my husband goes with me, but he said he wouldn’t.如果我丈夫能和我一起去, 我就出國,但是他說他不愿意.
The meeting would be put off in case it should rain. 若遇下雨, 會議延期舉行.