Other words to introduce a condition

We can use other words such as when, provided that, in case, so/as long as and unless instead of if in zero, first and second conditional sentences.

when; as soon as

We use when and as soon as instead of if to show that something is more likely:

I’ll give you a lift into town if I finish my work in time. (= I am not sure if I will be able to give you a lift)

I'll give you a lift into town when/as soon as I finish this work. (= I will give you a lift)

unless

We use unless to show a negative condition, with a similar meaning to if... not

You won't earn much interest unless you invest it properly. (= if you don't invest it properly)

provided/providing that, so/as long as

These phrases can be used instead of if for emphasis. Provided/providing that are more common in written than spoken English:

You won't lose any money provided that you think of it as a long-term investment. (= if you think)

As long as you get a second-hand car; you should still be able to invest some money. (= if you get)

In case

We use in case to talk about precautions. Compare:

You should keep this reference number in case there are any problems. (= keep the reference number because there might be problems later)

You should quote this reference number if there are any problems. (= quote this reference number at the time of any problems)

!!! We don't usually start a sentence with in case