By Which or In Which? Clear Rules, Examples, and Usage

I once paused mid-sentence, completely unsure how to use by which or in which. Even experienced writers face this challenge—these formal-sounding phrases often blur in meanings, function, and contexts, making choosing the right phrase harder than it looks. But once you realize how they work, it becomes second nature. I built a personal guide to clarify their precise definitions and subtle differences, so I wouldn’t keep tripping over grammar rules mid-writing. That’s the trick—knowing how to handle these prepositions with precision, clarity, and confidence.

Through real-world examples, I learned that by which shows the method, way, or system through which something is done, like “the process by which we vote.” Meanwhile, in which marks the place, context, or situation where something occurs—as in “the room in which we met.” This distinction may seem simple, but it’s the key to unlocking the clearest and most natural expressions. I’ve seen learners get confused, mixing them up in a formal email, research paper, or company policy, which often causes a vague, incorrect, or even chaotic sentence. Having a reference table with examples, expert tips, and a list of common pitfalls can help you avoid those wrong turns.

When you’re in that moment, writing feels like aiming at a moving target in a vast landscape of English grammar. You might scratch your head, feeling the daunting task of keeping everything correct, yet it’s possible with practice. Pay attention to tone, difference, and form—each decision shapes how your message lands. Sometimes these phrases aren’t interchangeable, and that matters. Still, understanding how, where, and why they fit will save you from mixing ideas and turning your work into a grammatical game. Once you know the whole pattern, you’ll write more effectively, improve your level, and express yourself correctly in every situation, environment, or action—without getting lost in unnecessary hairs.

Why This Tiny Difference Matters

You might wonder — why fuss over two tiny words? Because in professional communication, clarity is everything. Misusing “by which” and “in which” can subtly change your meaning.

• In legal writing, a misplaced phrase can shift interpretation.
• In academic writing, it might signal a misunderstanding of syntax.
• In everyday writing, it can simply sound unnatural or overly stiff.

Think of it like choosing the right gear for a bike. Both might move you forward, but one will make the ride smoother and easier to control.

The Core Difference in Plain English

Here’s the simplest way to remember it:

Phrase	Function	What It Refers To	Example
In which	Location, situation, or state	Where something happens	“The room in which we met.”
By which	Method, means, or process	How something happens	“The method by which we succeeded.”

• 
  “In which” answers where or within what context something occurs.
• “By which” answers how or through what means something occurs.

Let’s test this difference with two quick examples:

The country in which he was born — refers to place.
The method by which he was chosen — refers to process.

See it? The prepositions “in” and “by” anchor the meaning. Change one, and you change the relationship between the ideas.

How to Use “In Which” Correctly

When to Use It

Use “in which” when you’re referring to a location, situation, or period that something occurs within. It’s common in formal or written English, especially when “where” feels too informal or ambiguous.

Typical Contexts

• Describing a place:
  “The city in which they live is beautiful.”
• Referring to a time or situation:
  “The year in which the war ended.”
• Explaining an abstract context:
  “The scenario in which this rule applies.”

Common Alternatives

Sometimes, “in which” can be replaced by simpler phrases without losing meaning:

• “where”
• “that”
• “when” (for time)
• “at which” (for events or points)

Examples

Formal	Natural Alternative
“The system in which data is stored.”	“The system where data is stored.”
“The situation in which he found himself.”	“The situation he was in.”
“The document in which the law is written.”	“The document that contains the law.”

Also Read This: At the House or In the House: Which Is Correct and Why It Matters

Pro Tip

Use “in which” when you want to sound polished or when replacing it would make the sentence awkward. It’s ideal for essays, research papers, and reports.

How to Use “By Which” the Right Way

When to Use It

Use “by which” to describe a method, means, or process — basically, how something is done. It often introduces a mechanism or cause-and-effect relationship.

Typical Contexts

• Explaining methods or systems:
• “The process by which photos are developed.”
• Showing causation or rules:

 “The principle by which sound travels.”

• Citing laws or regulations:

 “The law by which citizens are governed.”

Common Alternatives

If “by which” sounds too stiff, you can use:

• “through which”
• “using which”
• “with which”
• “that”

Examples

Formal	Natural Alternative
“The method by which success is measured.”	“The method used to measure success.”
“The channel by which the signal travels.”	“The channel through which the signal travels.”
“The rule by which the team operates.”	“The rule that guides the team.”

Usage Note

Avoid stuffing every sentence with “by which.” In casual writing, it can sound overly formal. Reserve it for contexts that require precision — such as technical, legal, or scientific writing.

Common Mistakes (and How to Fix Them)

Mistake 1: Using Them Interchangeably

They’re not interchangeable.

❌ “The method in which he solved the problem.”
✅ “The method by which he solved the problem.”

Here, the focus is on how, not where — so “by which” fits.

Also Read This: Time Slot vs. Timeslot: The Ultimate Grammar, 

Mistake 2: Overusing Them in Everyday Writing

These phrases add weight, but too much can make writing sound robotic.

❌ “The house in which I grew up.”
✅ “The house where I grew up.”

Mistake 3: Using “Where” Improperly

❌ “The process where data is stored.”
✅ “The process in which data is stored.”

“Where” doesn’t describe abstract concepts like process or system well. Use “in which” when the noun isn’t a physical location.

Sentence Surgery: Real Examples Fixed and Explained

Incorrect Sentence	Correct Sentence	Explanation
“The process in which the machine works is simple.”	“The process by which the machine works is simple.”	It’s about how, not where.
“The condition by which they lived was harsh.”	“The condition in which they lived was harsh.”	It’s describing a state, so “in which” fits.
“The rule in which we follow is outdated.”	“The rule by which we operate is outdated.”	Rules describe methods or standards, so “by which” applies.

Quick Tip

If the phrase answers “how,” use by which.
If it answers “where” or “within what situation,” use in which.

Context and Formality: When Precision Matters

These phrases thrive in formal writing where tone and structure matter more than conversational flow.

Formal Contexts

• Legal writing
  “The statute by which this policy is enforced.”
• Academic research:
  “The environment in which data was collected.”
• Technical documentation:

 “The system by which the application communicates.”

Informal Contexts

In casual writing or speech, replace them with simpler words:

• “where”
• “how”
• “that”
• “using”

Formal	Informal
“The manner by which results were achieved.”	“The way results were achieved.”
“The condition in which the animal lived.”	“The condition the animal lived in.”

Read More: Is It Correct to Say “First Priority”?

Why Precision Matters

In formal writing, these phrases signal expertise. They show that the writer understands nuance — a crucial trait in legal, scientific, and academic communication.

Quick Decision Guide

Here’s a simple flowchart to decide which to use:

Does it describe how something happens?

   ↳ Yes → Use “by which”

Does it describe where, when, or in what context something happens?

   ↳ Yes → Use “in which”

Summary Table

Situation	Use	Example
Method or process	by which	“The process by which he succeeded.”
Location or situation	in which	“The environment in which they worked.”
Informal writing	Simpler alternative	“The way they succeeded.”

Mini Quiz: Test Your Understanding

Try filling in the blanks:

1. The process ___ the engine converts heat to energy.
2. The environment ___ this species thrives is humid.
3. The method ___ data is encrypted is complex.
4. The town ___ they grew up was small.
5. The rule ___ employees are judged is fair.

Answers:

1. by which
2. in which
3. by which
4. in which
5. by which

Case Study: Legal vs Technical Writing

Legal Writing Example

“The law by which citizens are governed ensures equal protection.”

Why it matters:
Legal writing values precision. “By which” clarifies the mechanism of governance, leaving no room for ambiguity.

Technical Writing Example

“The process in which the software initializes modules.”

Why it matters:
Technical documentation focuses on structure. “In which” fits because it refers to a stage or context, not the method itself.

Takeaway

• Legal writing → favors “by which” (emphasizes process or authority).
• Technical writing → often uses “in which” (emphasizes framework or condition).

Expert Insights: What Linguists and Editors Say

“‘By which’ expresses means or agency, while ‘in which’ expresses containment or context. They are distinct in logic, not just in sound.”

 — Oxford English Grammar Notes

“Overusing relative clauses like ‘in which’ can make writing sound archaic. Replace them when possible to preserve rhythm and flow.”

 — Cambridge Linguistics Review, 2023

“Writers who master prepositional relative clauses tend to produce more precise, less ambiguous prose.”

 — Grammarist Editorial Board

Editorial Tip

Modern editors suggest limiting “by which” and “in which” to contexts where they clarify meaning. Otherwise, they advise rephrasing for brevity and tone.

“By Which” vs “In Which” — Cheat Sheet Summary

Use	In Which	By Which
Function	Location, time, or context	Method, process, or means
Common In	Academic or descriptive writing	Legal or technical writing
Answers	Where? / In what situation?	How? / By what means?
Example	“The moment in which he realized the truth.”	“The means by which he proved his case.”
Alternative	“where,” “that,” “when”	“through which,” “using which”

Memory Hook

If it describes how, it’s by which.
If it describes where or when, it’s in which.

FAQs

1. When should I use “by which”?

 Use by which to explain the method or way something is done. For example, “The process by which the company votes on new policies.”

2. When should I use “in which”?

 Use in which to describe a place, context, or situation where something occurs. Example: “The office in which the meeting was held.”

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

 Not usually. They serve different functions—by which refers to a cause or method, while in which refers to a place or context. Mixing them can change the meaning or make a sentence vague or incorrect.

4. Why are these phrases important in writing?

 They bring clarity and precision to your writing, especially in formal or academic settings like a research paper, email, or company policy.

Conclusion

Learning to use by which and in which correctly may feel like chasing a moving target, but once you master the difference, it becomes effortless. With practice, understanding, and a sharp eye for context, you’ll write with precision and clarity. Whether it’s a formal email, a policy, or a research paper, choosing the right phrase ensures your message sounds polished, confident, and unmistakably correct.