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Hello,

I have to select either till or unless .

1. They are not allowed to play till/unless they finish their homework.

To me both seem ok.

2. You cannot cross the road till/unless the traffic light changes to green

To me both seem ok.

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

To me both seem ok.

4.They did not let me in till/unless I showed them my ticket.

To me both seem ok.

5. She won't get up till/unless someone shakes her.

To me both seem ok.

Please check and comment on it.
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Hanuman_2000Hello,

I have to select either till or unless .

1. They are not allowed to play till/unless they finish their homework.
To me both seem ok.
till: Okay. It implies from now until something is done.
unless: Better to add 'first' at the end. "Can't play unless HW is finished first."


2. You cannot cross the road till/unless the traffic light changes to green
To me both seem ok.
till: Okay.
unless: Better to say "Can't cross the road unless the traffic light is green."


3.You cannot go and play till/unless you finish your homework.
To me both seem ok.
See 1 above.

4.They did not let me in till/unless I showed them my ticket.
To me both seem ok.
till: okay
unless: They do not let you (one) in unless you (one)show them your (one's) ticket.


5. She won't get up till/unless someone shakes her.
To me both seem ok.
till: probably ok, but more appropriate if you want to say something like "She won't get up till noon."
unless: Better choice.


Please check and comment on it.
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Hi Hanuman

You seem to be struggling with the usage of "until" and "unless".

Until-clauses are time adverbial clauses to indicate the time at which the main clause's state stops. "Unless" is a rephrase of "if not" or "except if" and it is a clause to indicate the condition on which the main clause's event doesn't take place.

1. John will wait her until she gets married to other guy.
2. John will wait her unless she is married to other guy.
#1 means John's waiting her will stop when she gets married to other guys. #2 means John's waiting her doesn’t happen if she is married to other guy. What we have to note is that an until-clause commonly states an instantaneous event because it is to indicate a time point. On the other hand, an unless-clause commonly states a state because it is to indicate a condition.

3. You cannot play until you finish your homework.
4. You cannot play unless you finish your homework.
#3 is fine. It means the state of "being unable to play" will stop only when "you" finishes his homework. Here the speaker knows "you" has not yet finished his homework. So we cannot make a sentence like "You cannot play now until you finish your homework". #4 is wrong. Because the unless-cause is not a statement to indicate a future time point, it should be "You cannot play unless you have finished your homework". It means "You can play even now if you have finished your homework".

5. You cannot cross the road until the traffic light changes to green
6. You cannot cross the road unless the traffic light changes to green
The same discussion as given for #3 and #4 can apply to the pair of these sentences. #6 is wrong, but "You cannot cross the road unless the traffic light is green" is correct.

7. They did not let me in until I showed them my ticket
8. The did not let me in unless I showed them my ticket
#7 is fine. If we are more correct about the time sequence of the events in the two clauses, it would be "They hadn't let me in until I showed them my ticket", but it is a bit too formal. #8 is wrong because unless-clauses cannot be used to give a condition to the event in the past. One might make a sentence like "They wouldn't have let me in unless I had showed them my ticket". But in this case, we have to say "They wouldn't have let me in unless I had showed them my ticket".

9. She won't get up until someone shakes her.
10. She won't get up unless someone shakes her.
To me both of them sound fine. We may paraphrase #9 as "She will get up when someone shakes her". And we can paraphrase #10 as "She will not get up if someone does not shake her".

paco