/The use of 'by', etc. + agent after a passive\

**mrmreka** · 28-06-2010, 12:03 AM

The use of 'by', etc. + agent after a passive

An agent is a 'doer', i.e. the person or thing that performs the action indicated by the verb. By + agent in passive constructions tells us who or what did something

The window was broken by the boy who lives opposite
The window was broken by a stone

By + agent is only necessary when the speaker wishes to say (or the hearer has to know) who or what is responsible for the event in question. The position of by + agent at the end of a clause or sentence gives it particular emphasis

The window was broken by a slate that fell off the roof

Information can be given by means of phrases other than by + agent

This bridge was built in 1816/of stone/before the war. etc

By + agent is often used with the passive of verbs like build, compose, damage, design, destroy, discover, invent, make, wreck and write. Note how a question in the active is often answered by a passive, so that the important information (i.e. what the questioner wants to know) is emphasized by being at the end

Who composed that piece? - It was composed by Mozart
What destroyed the village? - It was destroyed by a bomb

Note the inclusion of by in questions with Who(m)

Who(m) was 'Bleak House' written by? - Dickens

With is often used with an agent, especially after past participles such as crammed, crowded, filled and packed

During the World Cup our streets were filled with football fans

But compare by + agent and with in: e.g

He was killed by a falling stone. (accidental
He was killed with a knife. (deliberate
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