Note that unless means if not and hence it would be wrong to use another not in clauses with unless. Study the following examples.
If- and unless-clauses are used to talk about a condition – something which must happen first so that something else can happen. In if and unless-clauses we use a present tense to refer to the future.
- She must consult a doctor. Otherwise she will not know what her problem is.
- If she does not consult a doctor, she will not know what her problem is.
- Unless she consults a doctor, she will not know what her problem is. (NOT Unless she does not consult a doctor she will not know what her problem is.)
- The typist should be careful. Otherwise she will lose her job.
- If the typist is not careful, she will lose her job.
- Unless the typist is careful, she will lose her job.
- He will have to make the payment in time. Otherwise his house will be confiscated.
- If he does not make the payment in time, his house will be confiscated.
- Unless he makes the payment in time, his house will be confiscated.
- You must use your time wisely. Otherwise you will not be able to do much.
- If you do not use your time wisely, you will not be able to do much.
- Unless you use your time wisely, you will not be able to do much.