Unless ha lo stesso significato di if...not. Come if, unless è seguito da una voce verbale al presente o al passato o al perfetto (mai da un condizionale). Unless può essere usato al posto di if...not in qualsiasi tipo di periodo ipotetico. L'ordine delle proposizioni è irrilevante quando si usa unless.
Periodo ipotetico 1: Unless + presente
| Con if | Equivalente con unless |
|---|---|
| You will be sick if you don't stop eating. | You'll be sick unless you stop eating. |
| I won't pay if you don't provide the goods immediately. | I won't pay unless you provide the goods immediately. |
| If you don't study dilligently, you'll never understand trigonometry. | Unless you study dilligently, you'll never understand trigonometry. |
Periodo ipotetico 2: unless + passato
| Con if | Equivalente con unless |
|---|---|
| If he wasn't very ill, he would be at work. | Unless he was very ill, he would be at work. |
| I wouldn't eat that food if I wasn't really hungry. | I wouldn't eat that food unless I was really hungry. |
| She would be here by now if she wasn't stuck in traffic. | She would be here by now unless she was stuck in traffic. |
Periodo ipotetico 3: unless + past perfect
| Con if | Equivalente con unless |
|---|---|
| Our director would not have signed the contract if she hadn't had a lawyer present. | Our director would not have signed the contract unless she had had a lawyer present. |
| I wouldn't have phoned him if you hadn't suggested it. | I wouldn't have phoned him unless you'd suggested it. |
| They would have shot her if she hadn't given them the money. | They would have shot her unless she'd given them the money. |