Prepositions: by and until

GLOW: Grammar Lessons On the Web
For the exclusive use of employees of the U.S. Department of State--by Tillyer Associates

Prepositions: by and until

By is a preposition with many uses and meanings.
Until is sometimes used as a preposition and is sometimes confused with by.

1. by is a preposition that means something like near or next to.

My father is the man standing by the window.

The library is by the post office downtown.

You can park your car by the red truck.

2. Another common meaning is past or along a line near.

The river flows by the village.

A bus goes by here every 15 minutes.

I knew she was angry when she walked right by me without even looking at me.

3. We also use by when we are talking about a way of doing things.

The new field officer arrived from Washington by plane.

I addressed the invitations by hand...I wrote each address myself.

We were notified of the changes by email.

I stepped on the gas instead of the brake by mistake.

An answer to a question might be just the prepositional phrase with by.

How did the field officer get here?	...by plane.
How were we notified of the changes?	...by email.

4. A similar use of by is when we talk about something or someone responsible for an action.

Have you ever been bitten by a snake?

We had the documents reviewed by an independent consultant.

Have you read the new book by Senator Haggerty?

5. Another use of by is when we speak of units of measurement.

The office staff gets paid by the hour.

The crowd got angrier by the minute.

We've been receiving applications for that position by the hundreds.

6. By, followed with a gerund, sometimes answers the question "How?".

How did you reach the ambassador?	We found him by calling his hotel.
How did you stop the attacker?	I stopped him by screaming loudly.
How did you offend the vice president?	... by arriving 20 minutes late.

7. We also use by with a reflexive pronoun to indicate that something was done without help or alone.

The staff had gone for the day so the boss had to type the speech by herself.

Since his wife was involved in some important meetings, the senator had to attend the reception by himself.

8. Finally, by means before or no later than a specified time.

I'm sorry to be late, I thought the meeting would be finished by 7:30.

Sergio is under a lot of pressure. He has to have this report written and typed by noon tomorrow.

All of the guests had left the reception at the mission by 8 p.m.

We have to get this place all cleaned up by the time Mr. Fairfax returns from Washington.

until

Until means up to a time or before. It can be followed by a time expression or an independent clause.*

There were visa applicants in our waiting room until 7 p.m.

They wouldn't leave until we turned off the lights.

We have until May 24th to finish the work.

Contrast the use of by and until.
We have to finish the work by midnight.	These two sentences mean the same thing.	We have until midnight to finish the work.
You must submit your application by May 1.	These two sentences mean the same thing.	You have until May 1 to submit your application.
Ambassador Haggerty gets to the office by 8 a.m.	The sentence with until has slightly pejorative (negative) meaning.	Ambassador Haggerty doesn't arrive at the office until 8 a.m.
The terrorists had left the building by the time the police arrived.	The sentence with by means the terrorists were gone when the police arrived. They were still there when the police arrived in the "until" sentence.	The terrorists stayed in the building until the police arrived.

* Technically, the word until, when followed by a clause, is a conjunction, but it means the same thing as a preposition.