prepositions by and from

Lilia from Bulgaria asks:

When do we use by and when do we use from?

For example, do we say:

• The decision has been approved by the committee. 
  OR
• The decision has been approved from the committee.

Thank you in advance for your explanation. 

  

'by' with passive clauses

In passive constructions, as in your example, the agent of the action is always introduced with the prepostion by, so the first one is correct.

We could turn the passive sentence into an active sentence if we wanted to use from and say:

• This decision has received approval from the committee.

But for all passive clauses we need to use by when introducing the person or thing responsible for the action:

• The walker was killed by a falling tree.
• All the roofs on the houses in the village were ripped off by the tornado.
• The visiting speaker was introduced by the club chairman.

The only exception to this is when we are talking about the tools used for the operation rather than the agent bringing about the action.

When we talk about the tools used for an action we say with rather then by.

Compare the following:

• She was killed with a kitchen knife.
• She was killed by an unknown assassin.
• The palace was built with red bricks from the local brickyard.
• The palace was built by a famous architect.

'by' to express time

By is used to indicate time up to a particular point:

• I want you to be home by eleven o’ clock (= before eleven OR at eleven at the latest).
• By the time I arrived, everybody had left.
• By the end of the lecture, nearly everyone was asleep.

by or near?

By also means very close to.

For example:

• Our house is quite close to the sea, but I would really like to live right by the sea.

'by' in common phrases

By is used in a number of common phrases.

Note the following:

• Are you going to deliver that parcel by hand, or will you send it by post?
• Do you want to pay for this in cash, by cheque or by credit card?
• You can get there by air, by road, by rail or by sea, but however you travel, I’m sure you’ll enjoy it.
• I have learnt this piece by heart and don’t need to have the music in front of me.

Note, however, if we put a determiner in front of the noun, it is no longer a set phrase and the preposition changes.

Compare the following:

• Why don’t you send it by email? It’s quicker.
• I learnt about it in an email from Richard.
• Did she come by car? 
  Yes, she did. She turned up in a brand new sports car!

from or since?

The preposition from indicates the starting point of an action. It is often used with to or till which indicates the finishing time of the action:

• I normally work from nine to five, sometimes from ten till six.
• You can drop by at any time during the afternoon. I shall be here from two onwards.
• From now on you must wear a suit and a tie whenever you go to the office.

Note that since is used with the present perfect or past perfect tense to indicate the starting point of the action. With other tenses we normally use from.

Compare the following:

• The office is open from eight o’ clock, but I don’t usually arrive before nine.
• I have been working on the project since the beginning of September and hope to finish it by the end of October.