BY: We only use “by + agent” when it is important to say who or what is responsible for something.


- The radio was invented by Marconi.

- A number of trees were blown down by the strong winds.

NOTE: We sometimes use the subject of an active sentence (Marconi, the strong winds) as ‘the agent’ in a passive sentence. When this happens, we use “by” to introduce the agent in the passive.

WITH: We use “with” to talk about an instrument which is used by the agent to do something.


- I was hit with an umbrella.

- The World Trade Center was crashed with two aircraft.

NOTE: We also use “with” to talk about materials or ingredients.


- The room was filled with smoke.

- Irish coffee is made with whiskey.