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.