Two phrases that confuse many writers are “by which” and “in which.”

This guide explains when to use each phrase.

By Which vs In Which: What’s the Real Difference?

The main difference lies in the preposition you need. The choice depends on what verb or context comes before it.

“By which” shows how something happens. It indicates the method, process, or means of doing something. Think of it as answering “how?”

“In which” shows where or when something happens. It indicates location, situation, or circumstances. Think of it as answering “where?” or “when?”

The preposition must match the verb naturally. For example, you say “achieved by” not “achieved in.” Similarly, you say “situated in” not “situated by“

When to Use “By Which” (Rules + Examples)

Use “by which” when you’re describing a method or process. It explains how something was accomplished or measured.

Common verbs that pair with “by which” include:

• Achieved
• Measured
• Determined
• Identified
• Calculated
• Established

Here are practical examples:

The method by which we solved the problem was innovative.
This sentence explains how the problem was solved.

She developed a system by which employees could track their hours.
The system is the means of tracking.

The criteria by which candidates are judged include experience and skills.
This shows how judgment happens.

Scientists discovered the process by which cells regenerate.
The process explains how regeneration occurs.

The formula by which interest is calculated appears on page five.
The formula is the method of calculation.

When to Use “In Which” (Rules + Examples)

Use “in which” when describing a location, time period, or circumstance. It sets the scene for your statement.

“In which” commonly follows these patterns:

• Places and locations
• Time periods and eras
• Situations and conditions
• States of being

Examples

The house in which I grew up was sold last year.
This specifies the location where growing up happened.

We live in an era in which technology dominates daily life.
The era is the time frame.

The situation in which we found ourselves was difficult.
This describes the circumstances.

She described the manner in which the accident occurred.
The manner refers to the conditions.

The container in which the samples are stored must be sterile.
This indicates the location of storage.

The year in which they married was memorable for many reasons.
The year is the time frame.

Wrong: The building by which we work is new.
Right: The building in which we work is new.

You work inside a building (location), so “in which” is correct.

Wrong: The strategy in which we won the game was brilliant.
Right: The strategy by which we won the game was brilliant.

The strategy is the method of winning, so “by which” is correct.

Common mistakes happen when writers forget to match the preposition with the main verb. Always ask yourself: Does the verb naturally take “by” or “in”?

For instance, you say “interested in” not “interested by.” Therefore, write “The subject in which she was interested” not “by which.”

Common Expressions and Idioms Using By Which and In Which

Expressions with “by which”:

The degree by which something changes appears often in scientific writing. Example: “The degree by which temperatures rose surprised researchers.”

The extent by which performance improved shows measurement. Example: “The extent by which sales increased exceeded expectations.”

The mechanism by which a process works explains function. Example: “The mechanism by which the drug operates remains unclear.”

Expressions with “in which”:

The world in which we live describes current conditions. Example: “In the world in which we live, digital skills are essential.”

The context in which something occurs provides background. Example: “The context in which the statement was made matters greatly.”

The environment in which growth happens sets the scene. Example: “The environment in which children learn affects outcomes.”

Academic Writing Tip: Formal writing favors these phrases over simpler alternatives. Instead of writing “how it works,” academic papers say “the manner by which it operates.”

FAQ’s

What is the difference between “by which” and “in which”?

“By which” refers to the method or means something happens, e.g., “This is the tool by which we measure temperature.”
“In which” refers to the place, situation, or context, e.g., “The room in which we met was very cozy.”

When should I use “by which” in a sentence?

Use “by which” to indicate the method, process, or agent of an action. Example: “He devised a plan by which we could save time. It highlights how something is done.

When should I use “in which” in a sentence?

Use “in which” to indicate location, time, or context. Example: “There was a situation in which everyone agreed to help.” It highlights where or in what context something occurs.

Can “by which” and “in which” be used interchangeably?

No. They have different grammatical roles. “By which” focuses on method, while “in which” focuses on location or context. Mixing them can make a sentence incorrect or confusing.

Are “by which” and “in which” formal or informal expressions?

Both are considered formal English and are common in academic, professional, and written contexts. In casual speech, people might rephrase sentences to avoid these constructions.

Conclusion

The choice between “by which” and “in which” depends on meaning. Use “by which” for methods and processes. Use “in which” for locations and circumstances.

Match your preposition to the main verb naturally. Practice with real examples helps you master this distinction quickly.