If & Unless

 

Type of 1 Conditional - unless+present tense

With - if 

1. If you don't study dilligently,  you'll never understand trigonometry.

2. You will be sick if you don't stop eating.

3. I won't pay if you don't provide the goods immediately. 

Equivalent with unless

1. Unless you study dilligently, you'll never understand trigonometry.

2. You'll be sick unless you stop eating.

3. I won't pay unless you provide the goods immediately.

Type 2 conditional: unless + past tense

1. If he wasn't very ill, he would be at work. 

2. I wouldn't eat that food if I wasn't really hungry. 

3. She would be here by now if she wasn't stuck in traffic.

Equivalent with unless

1. Unless he was very ill, he would be at work.

2. I wouldn't eat that food unless I was really hungry.

3. She would be here by now unless she was stuck in traffic.

Type 3 conditional: unless + past perfect

With - if

1. They would have shot her if she hadn't given them the money.

2. Our director would not have signed the contract if she hadn't had a lawyer present.

3. I wouldn't have phoned him if you hadn't suggested it.

Equivalent with unless

1. They would have shot her unless she'd given them the money.

2. Our director would not have signed the contract unless she had had a lawyer present.

3. I wouldn't have phoned him unless you'd suggested it.