​WHICH WORD?

By / Until

Used with "time"
for specific situations related to “time”.

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by

• not later than
  (a specified time) 
  
  
• something could be completed before
  ​(a specific time)

EXAMPLES:
​

1. The operation will be completed by 10:00 pm. It might be completed before 10:00 p.m. 
   
   
2. We will arrive in Miami by 6:00 a.m. We might arrive sooner, but for sure not after 6:00 a.m.  
   
   
3. I’ll be there by 5. I might arrive earlier than 5, but not after.  
   ​
4. I hope to learn English by the time I finish the university. Maybe I will learn it before.

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until

• up to
  (a particular time)
  ​
• a period of (specific time) 

EXAMPLES:
​

1. I’m going to study English tonight until 10, and then I will go out for a beer. 
   From now –> 10 you will be studying.
   
   
2. He will study for the test for 3 hours.  From 3:00 p.m until 6:00 p.m.
   
   
3. I will stay at the party until it is over.
   
   
4. I will study English until I learn it.

Note: By

Usually answers the question “When” in the future tense.

• When will the project be finished?  
  By November.
  
  
• When will you arrive at the party?  
  By 6 for sure.
  
  
• When will you call me?  
  By Thursday.  I promise.
  ​

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​NOTE: Until

Usually answers the question "How long"

• How long will you be working on the project?  
  Until November.
  
  
• How long will it take you to finish the report?    
  Until 3 this afternoon.
  
  
• How long were you in New York?    
  Until it started snowing then I went to Florida. 

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Grammar

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