Unless, Provided That and As Long As: Rules and Examples

Unless means except if or if... not. The verb after unless is affirmative, but the meaning is negative: I'll go unless it rains = I'll go if it doesn't rain. Don't add another not after unless, or the sentence will mean the opposite.

Unless works best when the main clause describes what will happen in all cases except one: You can't come in unless you have a ticket. It often appears in warnings, threats and rules. For the future, use the present simple after unless, just as in the first conditional.

Unless and if not are often interchangeable, but not always. Unless introduces an exception. If not can also introduce a reason or a cause. Compare: I'll be surprised if he doesn't come (the surprise depends on him not coming, so unless sounds wrong) and I'll be at home unless I have to work (staying home is normal; work is the exception).

Use if not, not unless, when the sentence expresses a feeling caused by something not happening, in most questions, and usually in third conditional regrets about the past: If I hadn't overslept, I wouldn't have missed the train.

These phrases mean only if. They stress that the condition is necessary: the result happens only when the condition is met. Provided that and providing that are a little formal, and that is often left out: provided you pay on time. On condition that is formal and usually describes a rule, a promise or an agreement.

The tense rules are the same as for if. Use the present for real future conditions, and the past simple for unreal ones: The bank would lend us the money provided that we had a guarantor.

As long as means only if, and it is the most common choice in everyday speech. So long as means the same but sounds a little more old-fashioned or formal. Both often express permission with a condition, or a reassurance: It doesn't matter what you wear, as long as you're comfortable.

Do not confuse this meaning with as long as for time (Stay as long as you like, which means for the whole time that) or with length (The river is as long as the Nile).

In case looks like a condition word, but it means something different: we do something now because something might happen later. Take a jacket in case it gets cold means take it now, before you know whether it will be cold. Compare: Take a jacket if it gets cold means wait, and take it only when it is cold.

Use the present simple after in case for the future, and the past simple for past precautions: I took a jacket in case it got cold. In American English, in case can also simply mean if (In case you need me, I am in my office), but the precaution meaning is the one to learn first.

Suppose, supposing and what if ask someone to imagine a situation. They often start a question. Use the present for a real possibility and the past for something less likely or imaginary, as in the second conditional: Suppose you lose your passport? Suppose you lost your passport?

Even if means that the result is the same whether the condition is true or not: I'll go even if it rains. It is stronger than if. Do not confuse it with even though, which talks about a fact: I went even though it was raining (it really was raining).

In everyday speech, people use unless, as long as and in case all the time, especially when they make plans, give permission and set rules. Provided that and on condition that are more typical of contracts, terms and conditions, formal emails and news. Learn which ones are spoken and which are written, and use them to sound more precise than if alone.

You will also hear short replies like Unless you'd rather stay in? and As long as it's not too late. For a wider look at conditionals, see wish and if only and the zero conditional.