We use several different structures to express a condition in English. The most common among these structures are explained here.

By using if

If is commonly used to express a condition. Examples are given below:

If you give respect, you get respect.
If you heat ice, it melts.
If you had asked him, he would have helped you.
If he worked hard, you would pass the examination.

Note that if is sometimes omitted in conditional clauses. In that case, we begin the sentence with the auxiliary verb had, should or were.

Compare:

If I were you I wouldn’t waste this opportunity.
Were I you, I wouldn’t waste this opportunity.

If you had been there we could have sorted the things out.
Had you been there we could have sorted the things out.

If you meet my brother tell him that I have passed the test.
Should you meet my brother tell him that I have passed the test.

By using unless

Unless is also used to express a condition. Note that unless means if not.

Unless you agree to my terms and conditions, you can’t expect any help from me. (= If you do not agree to my terms and conditions, you can’t expect any help from me.)
Unless you take the medicine, you can’t get well. (=If you do not take the medicine, you can’t get well.)
Unless you work hard, you will not pass. (=If you do not work hard you will not pass.)

By using an imperative

Sometimes we express a condition by using an imperative.

Take one step further and see what happens.

By using a conjunctional phrase

A condition can be expressed by using conjunctional phrases such as in case.

In case it rains, I shall put on my rain coat.
In case you are not satisfied with the product, you can send it back.

By using a participial phrase

Supposing you don’t win the prize, what will you do?
I will buy the house provided that it is in good condition.

Note that the same idea can be expressed in several different ways. Study the examples given below:

I will buy that house if it is in good condition.

I will not buy that house unless it is in good condition.
In case that house is in good condition I will buy it.
Supposing the house is in good condition, I will buy it.