(1) 这些词语均可用作连接词，由它们引导的从句中所要求的动词形式也相同。as/so long as, provided, providing, on condition that强调该满足的条件，if, assuming that, supposing (that)则侧重假设的情况。

• You'll certainly pass the examination if/as long as/providing/provided/on condition that you study harder.
  如果/只要你再用功一些，你肯定能考及格。
• I'll give you the day off on condition that you work on Saturday morning.
  只要你在周六上午加班，我就给你一天的假。
• You're welcome to stay with us, on condition that you share the rent with us.
  只要你与我们一起分担房租，欢迎你和我们同住。
• You can borrow my bike if/as long as/provided/providing/on condition that you bring it back before we knock off.
  只要你能在我们下班前回来，你就可以借我的自行车。
• Supposing/Assuming (that) he can't come, who will do the work? (=If he can't come, who will do the work?)
  假如他不能来，谁来干这项工作？
• Supposing/Assuming the plane is late? (=What is to be done if it is late?)
  假如飞机晚点怎么办？

 (2) supposing也可用虚拟语气。

• Supposing/If you fell in love with your boss, what would you do?
  假如你爱上了你的老板，你会怎样做？

 (3) 但有时if却不能用其他几个词语代替。

• You may spoil the whole plan if you fail to do your part.
  如果你不能尽你的责任，你可能会毁了整个计划。