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Hello,

1. My brother doesn't watch television till/unless he has got nothing else to do.

2. You cannot go and play unless/till you finish your homework.

3. You cannot travel till/unless you have a ticket.

4. She is going now unless/till you want her to stay.

I have to select either "till" or "unless".

I am very much confused about the usage of these two words .

Could anybody help me to clear my doubts?

Please I need your expert opnion about the usage of "till" and "unless".
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"till" (another way of saying "until") means "and that continues up to the point in time when".
"unless" means "except if" or "except in the case where/when".

[ A ] My brother doesn't watch television ----

and he continues not to watch television up to the point in time when

he has got nothing else to do.

[ B ] My brother doesn't watch television ----

except in the case where

he has got nothing else to do. (In that case, he does watch television.)

Which makes more sense? [ A ]? Or [ B ]?

To me, [ A ] makes no sense at all, and [ B ] is completely understandable, so [ B ] ("unless") is the correct answer.

CJ
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Until-clauses demand a state or a continuous act for the main clause. What is tricky in using "cannot" in the main clause is that "cannot" (=be unable to) can connote a state.

I cannot play until I finish homework.
=I can play when I finish homework.
I can play unless I have homework.
=I can play if I do not have homework.
(=I cannot play if I have homework.)
[Note that "finish" is a dynamic verb and "have" is a stative verb]

You cannot travel until you get a passport.
=You can travel when you get a passport.
You cannot travel unless you have a passport.
=You cannot travel if you do not have a passport.
(=You can travel if you have a passport.)
[Note that "get" is a dynamic verb and "have" is a stative verb]

I will wait you until you call me.
=I'll stop waiting you when you call me.
[Note that "call" is a dynamic verb]
I will wait you tomorrow unless you call me this evening.
=I will wait you tomorrow if you don't call me this evening.
(=I will not wait you tomorrow if you call me this evening.)
[Here the condition is "if 'I' have been called by "you' or not"]

paco
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Comments  
Hello Mr. CJ,

Once again, a fantastic explanation. Now, I am a bit confident. Let me try. My answers are in the braces.

1. You cannot go and play unless/till you finish your homework. (till)

2. You cannot travel till/unless you have a ticket.(unless)

3. She is going now unless/till you want her to stay. (unless)

------------------------------------------------

New doubts.

4. I will wait till you call me. (I will wait and it will be continue up to the point in time when you call me.)

5. I will wait unless you call me. ( I will wait except in the case you call me.(In that case, I will not wait.)

Both (5) and (6) seem right to me.

Please check it and comment on it.
Hello Mr. CJ

correction; Not (5) and (6) , but (4) and (5)

1. You cannot go and play unless/till you finish your homework. (till)

Is "unless" possible here?
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hanuman,
All your comments show that you have understood the difference between "unless" and "until".
You mention cases where both are possible, and you are right. There are many times when either one makes sense.
CJ
 paco2004's reply was promoted to an answer.