Read the following sentences.
- You must finish the job in time. Otherwise you will be sacked.
These two sentences can be joined using if or unless. Note that unless means if not and hence it would be wrong to use another not in clauses with unless.
- If you do not finish the job in time, you will be sacked.
- Unless you finish the job in time, you will be sacked.
- You must not violate the rules. Otherwise you will be in trouble.
- If you violate the rules, you will be in trouble.
- Unless you violate the rules, you will not be in trouble.
- He will have to work hard. Otherwise he will not pass.
- If he does not work hard, he will not pass.
- Unless he works hard, he will not pass.
- The boys must reach school in time. Otherwise they will be punished.
- If the boys do not reach school in time, they will be punished.
- Unless the boys reach school in time, they will be punished.
- You must not reveal secrets. Otherwise your friends will not trust you.
- If you reveal secrets you friends will not trust you.
- Unless you keep secrets, your friends will not trust you.
Notes
Note that in clauses with if and unless, we use a present tense to refer to the future.
If you do not work hard, you will not pass. (NOT If you will not work hard, you will not pass.)
Unless you work hard, you will not pass. (NOT Unless you will work hard, you will not pass.)