这几个连词用虚拟语气的较为普遍,但也要看具体情况.
1、 有时候表示事实相符的真实语气,如：
We shall go provided that the weather is fine 只要天晴, 我们就去.
Suppose he can't come, who will do the work? 如果他不能前来, 谁来做这项工作呢?
I will lend you the book on condition that you return it on Monday. 如果说你能在星期一还我,我可以借给你这本书.
2、多数情况下表示与事实相反的虚拟语气,如：
Provided it was fine we would have a pleasant holiday. 如果天气好, 我们的假日真的有可能过得非常愉快（但是事实不是如此）.
Supposing your father saw you now, what would you say?退一步说你父亲现在看到了你, 你该怎么说?
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, 我就出国,但是他说他不愿意.
The meeting would be put off in case it should rain. 若遇下雨, 会议延期举行.