What is the difference between by and with?

'By' shows the agent (who/what caused something) in passive sentences: 'The window was broken by a ball.' It also shows method of travel: 'by car, by bus.' 'With' shows the tool or instrument: 'The window was broken with a hammer.' It also means accompanied: 'I came with my friend.'

Is it 'killed by a knife' or 'killed with a knife'?

Both are possible but mean different things. 'Killed by a knife' treats the knife as the agent/cause. 'Killed with a knife' treats the knife as the instrument/tool used. In practice, 'stabbed/killed with a knife' (tool) is the more natural choice, while 'by' is typically used for people or forces of nature.

How do you use 'by' for transport?

Use 'by' without an article to talk about means of transport: 'by car,' 'by train,' 'by plane,' 'by bus.' Do NOT say 'by the car' or 'by a bus' in this context.

By vs. With: What's the Difference?

Quick Answer

By = the agent (who did it), method, or means of transport: "written by Shakespeare," "travel by train"
With = the tool/instrument, or accompanying someone/something: "cut with a knife," "came with my friend"

Explanation

BY

1. Passive voice, agent (who/what did the action):

"The book was written by Hemingway."

2. Means of transport (no article):

"I travel by car / bus / train / plane."

3. Method of communication:

"Send it by email / post."

4. Deadline:

"Please finish it by Friday."

WITH

1. Tool or instrument (what was used):

"She cut the bread with a knife."

2. Accompaniment (together with):

"He came with his family."

3. Having / possessing a characteristic:

"A room with a view." / "A man with blue eyes."

4. Emotions/reactions:

"She trembled with fear." / "He smiled with joy."

Key Distinction: Agent vs. Tool

In passive sentences, use by for the person or force that did the action, and with for the instrument or tool used:

"The door was locked by the security guard with a key."

"He was attacked by a stranger with a stick."

Examples

✔The painting was created by Picasso. (agent)

✔He painted it with a special brush. (tool)

✔I go to work by bus. (means of transport)

✘I go to work with bus. (means of transport takes "by")

✔I came to the party with my sister. (accompanied by)

✘The letter was written with a famous author.

✔The letter was written by a famous author.

Common Mistake

Incorrect: The homework was done with the student.

Correct: The homework was done by the student.

In passive sentences, the person performing the action takes by, not with.

Practice

Choose the correct word:

"The report was submitted _____ email _____ the manager." (by / with)