Prepositions of Agent & Instrument

Expressing WHO or WHAT performed an action

Sections
Introduction

1. Definition & Core Meaning

Prepositions of Agent and Instrument tell us who performed an action (agent) or what was used to perform it (instrument).

What is it?
Expressing WHO or WHAT performed the action

2. Use Cases

WordMeaningExample
byThe person/thing that performed the action (passive voice)"This play was written by Shakespeare." / "She was bitten by a dog."
withThe tool, object, or instrument used"He cut the rope with a knife." / "She painted with a brush."
withoutIn the absence of a tool or person"She finished the project without any help." / "He ate without a spoon."

3. When to Use It (Time Expressions/Signals)

[!NOTE]
by is the key preposition of agent in passive sentences. with is for tools and instruments.

4. How to Use It (Rules)

  • Use by in passive constructions to introduce the agent (doer)
  • Use with to introduce the instrument (tool) used
  • Use without to show the absence of a tool or helper
  • by can also mean "via a method": by car, by email, by hand