Words for Condition

A.
1. You can't get in unless you have a ticket
2. You can use this book on condition that you return it by 5:00
3. In case of fire, dial 911.
4. You can stay as long as you don't mind sleeping on the sofa.

as long as : the least formal
on condition that : the most formal
providing that/provided that : a little more formal

In 3, don't confuse in case of with in case. "Take your unbrella in case it rains." [It isn't raining, but there's a chance of rain today.]

B. possibility with supposing/suppose and what if.
Supposing/Suppose and What if express possible situations in the future. (usually in spoken language).

- Supposing/Suppose it rains tonight - will the baseball game be called off?
- What if he doesn't turn up - what will we do then?

C. conditions with -ever
However you do it, it will cost a lot of money.
You'll get to the rain station, whichever bus you take.
Whoever wins the election, nothing will really change.
That box is so big, it will be in the way wherever you leave it.

These four sentences can also be expressed using no matter.

No matter how you do it, it will cost a lot of money.
You'll get to the train station no matter which bus you take.

D. Some nouns that express condition
Certain conditions must be met before the peae talks can begin.
Proficiency in English is a prerequisite for admisison to an American university. [absolutely necessary; a formal word]
What are the requirements for obtaining a driver's licence? [official conditions]
I would not move to a big city under any circunstances. I hate big cities!