Prepositions of Agent & Instrument

In English grammar, prepositions of agent and instrument are used to express the relationship between an action and the doer (the agent) or the tool/method used (the instrument) to perform that action.

These prepositions are highly common, especially when writing in the passive voice or explaining how a process is completed.

1. Prepositions of Agent (Who performs the action?)

A preposition of agent shows who or what is responsible for an action. The most common preposition used for this is By.

Using “By” for Agents:

  1. Primarily used in passive voice sentences to introduce the performer of the action.
  • The Harry Potter books were written by J.K. Rowling.
  • The cake was decorated by my sister.
  1. Can also refer to forces of nature or inanimate causes acting as agents.
  • The town was destroyed by a flood.
  • The email was sent by the system administrator.

2. Prepositions of Instrument (What tool or method is used?)

A preposition of instrument shows the tool, device, body part, or method used to achieve a result. The most common prepositions for this are With and By.

A. Using “With” for Tools and Instruments:

We use with when we talk about physical tools, instruments, or body parts that a person uses consciously to perform an action.

  • I cut the bread with a sharp knife.
  • He wrote the letter with a red pen.
  • She pointed to the sign with her finger.

B. Using “By” for Methods, Transportation, and Communication:

We use by (often without articles like a or the) to show the method, medium, or mode of transport used.

1. Transportation:

  • I travel to work by train. (Not by the train).
  • They sent the goods by air.

2. Methods/Means:

  • You can pay by credit card.
  • She succeeded by working hard.

3. Communication:

  • We contacted them by email.

Key Difference: By vs. With

It is easy to confuse by and with. Remember this simple rule:

  • Use by for the creator or performer (agent) or general method.
  • Use with for the specific tool or object (instrument) used by the performer.

Comparison:

  • The window was broken by the boy. (The boy is the agent).
  • The window was broken with a baseball. (The baseball is the instrument).

Complete Sentence Examples

Here are more examples of prepositions of agent and instrument in actions:

  1. The song was performed by a famous band.
  2. She opened the lock with a hairpin.
  3. We clean the floor with a mop.
  4. The database was updated by the developer.
  5. He was hit by a falling branch.
  6. Can we send the documents by fax?
  7. They built the house with their own hands.
  8. The fire was extinguished by firefighters with water.

Next, we will explore Prepositions of Cause, Purpose & Reason to learn how to express why actions occur.