From Longman Dictionary of Contemporary Englishunlessun‧less /ʌnˈles, ən-/ ●●●S1W1 conjunction 🔊 🔊 1IFused to say that something will happen or be true if something else does not happen or is not true 🔊 Unless some extra money is found, the theatre will close. 🔊 I think you should complain – unless, of course, you are happy with the way things are. 🔊 He won’t go to sleep unless you tell him a story. 🔊 I can’t leave her unless I know she’s all right.► see thesaurus at if2 →not unlessGRAMMAR: Choosing the right tense• You use the simple present tense with unless: Unless the government changes its policy, the economic situation will get worse.• Don’t use ‘will’ in the clause after unless. ✗Don’t say: Unless the government will change its policy ...• You can also use the present perfect tense with unless: I won’t change anything unless someone has asked me to.✗Don’t say: unless someone will have asked me to | unless someone will ask me to• To talk about the past, use the simple past with unless: Unless the company got a loan, it would go bankrupt.They threatened to kill him unless he gave them the money.✗Don’t say: Unless the company would get a loan ...USAGE: Unless, in case, or else•You use unless when saying that if something does not happen, something else will happen: Unless I hear from you (=if I don’t hear from you), I’ll assume everything’s OK.•You use in case when saying that you do something in order to be prepared if something happens: Take a sweater in case you get cold.•You use or else when saying that something bad will happen if you do not do something: You’d better go now, or else you’ll miss the train.