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Date: 1400-1500
Origin: on less than 'on a lower condition than' (1400-1500)

unless

conjunction
     
un‧less S1 W1
1 used 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 usage note except1
2

not unless

only if:
'Will you go with her?' 'Not unless she wants me to.'
WORD CHOICE: WORD CHOICE:

unless, if ... not, in case, or (else)
Use unless to say that something will happen or be true if something else does not happen or is not true Unless they get protection, they will not testify.!! Do not use the future tense after unless I won't go unless you go (NOT unless you will go).!! Do not say 'unless if' Don't call him unless it's urgent (NOT unless if it's urgent). Use if ... not when you know that something did not or will not happen If he had not tripped, he would have won (=but he didn't win). | I would go out if it wasn't raining (=but it is raining, so I am not going out). Use in case when talking about something that is or should be done because something might happen Take a sweater in case you get cold (NOT unless you get cold). Use or or or else to say what bad thing will definitely happen if something else does not happen You'd better go, or else you'll miss the train (NOT unless you miss the train).
WORD CHOICE: WORD CHOICE:

except, besides, apart from, unless
except means 'not including' or 'but not' They invited everyone except Julie.besides means 'in addition to' Besides Italy (NOT except Italy), I would like to visit France and Spain.apart from can be used with either meaning I ate everything apart from (OR except) the soup. What do you like doing apart from (OR besides) swimming?except is not used to introduce another clause. Use unless or except if, except when, except while, except that We won't go unless you really want to (NOT except you really want to). I cycle to work, except when it rains (NOT except it rains). In spoken English, people sometimes leave out 'that' The play went well, except (that) a few people forgot their lines.See also except

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