If, Not and Unless

l Imagine that Margie’s mother told her, “You’ll feel awful if you don’t finish your history lesson.”

l She could also say: “You’ll feel awful unless you finish your history lesson.”

Unless means if not. Sentences with unless or if not are negative conditional sentences.

Notice that these sentences have two parts. The part that begins with if not or unless tells us the condition. This part has a verb in the present tense (look at the verbs don’t finish, finish in the sentences above).The other part of the sentence tells us about a possible result. It tells us what will happen (if something else doesn’t happen). The verb in this part of the sentence is in the future tense (you’ll feel/you will feel).

Notice these two tenses again in the following examples :

Complete the following conditional sentences : Use the correct form of the verb.

3. Unless you promise to write back, I ..........