“By Which” vs “In Which”

In the language world, tiny differences carry a lot of weight. I’ve met people who’ve paused, mid-thought or even mid-sentence, wondering if they should say “by which” vs “in which“. Though these phrases look similar, their meaning is very different. “By which” usually explains a method or cause, while “in which” refers to a place, situation, or condition. That small nuance can shape the clarity of your sentence. And yes, it matters, especially in professional writing.

As a language editor, I’ve seen how a simple swap between these two can change the tone of entire documents. That’s why I built a handy guide, my manual on using them correctly and confidently. It comes with examples, grammatical notes, quick breakdowns, usage tables, and some helpful idioms to make the lesson stick. After regular practice, your linguistic instincts become sharper, and your inner grammar sense kicks in. One day, you’ll catch yourself choosing the right form like it’s a natural superpower.

Why “By Which” vs “In Which” Are Commonly Misused

Ever feel like grammar rules are like walking through a minefield blindfolded? You’re not alone. Phrases like “by which” and “in which” are easy to confuse because they look alike, sound formal, and often appear in contexts where precision matters- academic papers, legal documents, research studies, and even formal business emails.

But here’s the deal: The difference between them lies in what they convey.

• “By which” expresses method, means, or cause.
• “In which” expresses location, time, or condition.

Let’s break them down step-by-step.

Understanding the Grammar Behind the Phrases

To grasp the difference, we need to understand how these phrases are constructed.

• “By” and “in” are prepositions.
• “Which” is a relative pronoun.

Together, they introduce relative clauses- subordinate clauses that give more detail about a noun.

The law by which the decision was made…
The environment in which the animals thrived…

These aren’t just fancy structures- they serve specific functions in formal English.

What “In Which” Means (And When to Use It)

Definition:

“In which” is used when referring to a situation, condition, or location.

It typically replaces “where” in more formal contexts.

Examples:

• The era in which he was born shaped his views.
• This is the lab in which the experiment took place.
• The folder in which I saved the files is missing.

Think of “in which” as a more precise version of where, especially in writing that demands clarity.

Situations Where “In Which” Works Best:

Use Case	Example	Alternative
Periods	The decade in which jazz flourished…	The decade where… (less formal)
Locations	The city in which I studied abroad…	The city where…
Abstract Concepts	The context in which it happened…	Where it happened…

💡 Tip: Use “in which” in formal writing, like research papers, legal statements, grant proposals, or professional reports.

What “By Which” Means (And When to Use It)

Definition:

“By which” refers to the means, cause, or method through which something happens.

It answers the unspoken question: How?

Examples:

• How they escaped remains unclear.
• The channel by which the funds were transferred is under review.
• The mechanism by which plants convert sunlight…

When you see “by which,” think process, method, or path.

Best Use Cases for “By Which”:

Function	Example	Explanation
Method	The technique by which data was gathered…	Shows the method
Cause	The conditions by which laws are enforced…	Shows a causal relationship
Instrument	The system by which this works…	Shows how something functions

🧠 Grammar Note: “By” shows agency. It’s about the thing doing the work or causing the result.

“Wherein” vs. “In Which”: Same Thing or Not Quite?

Wherein is an old-school word meaning “in which.” You’ll still see it in legal documents, scholarly articles, and certain types of formal writing, but it’s less common in modern usage.

Examples:

• The contract wherein the terms are defined…
• The situation wherein we found ourselves…

When to Use “Wherein”:

Phrase	Modern Alternative	Formality Level
Wherein	In which	Very formal
Where	In which	Neutral to casual
In which	–	Formal and versatile

✨ Use “wherein” when writing for legal, historical, or academic audiences. Otherwise, “in which” gets the job done without sounding archaic.

When to Use “Where” Instead of “In Which”

Sometimes you don’t need either phrase. “Where” can replace “in which” in casual or spoken English.

Side-by-side comparison:

Formal	Informal
The village in which he was born…	The village where he was born…
The case in which the error occurred…	The case where the error occurred…

Key Differences:

• Where = informal, spatial
• In which = formal, specific, adaptable beyond location

Choose “where” in blogs, emails, or speeches.
🧑‍⚖️ Choose “in which” in reports, essays, and legal writing.

Common Pitfalls and How to Avoid Them

Here are some mistakes people often make- and how to fix them.

Mistake: Misplacing the Preposition

“The method the data was collected…” → Awkward

Better:

“The method by which the data was collected…”

Mistake: Overusing “Where” in Formal Writing

“The context where it happened…” → Too informal for a legal doc

Better:

“The context in which it happened…”

Examples: “By Which” vs. “In Which” Side by Side

Let’s compare both in real contexts:

Sentence	Phrase Used	Why It Works
The framework by which the rules are enforced is outdated.	By which	It describes a method or system
The society in which they lived valued loyalty.	In which	It describes a setting or condition
The process by which oil is refined…	By which	It explains the method
The environment in which coral thrives…	In which	It describes a location or condition

Real-World Case Study: Legal vs. Journalistic Language

Legal Brief Example:

“The contractual agreement wherein the tenant waives liability…”

Why it’s used: Legal docs require formality, precision, and airtight phrasing. “Wherein” fits like a glove here.

News Article Example:

“The town where the tragedy happened was already under pressure…”

Why it’s used: Journalistic writing aims for readability. “Where” feels natural, conversational, and less stiff.

Tone and Context: Choosing the Right Phrase for the Job

Language should fit the room. Here’s how to decide:

Audience	Preferred Phrase
Academic committee	“In which” or “By which”
Judge or legal team	“Wherein” or “By which”
Blog readers or coworkers	“Where” or “How”
Scientific journal	“By which” (for process), “In which” (for condition)

🎯 Rule of Thumb: If the sentence is about how to use “by which.” If it’s about where or when, use “in which.”

Quick Reference Table: Know Which One to Use

Phrase	Function	Best Used In	Example
In which	Location, time, or condition	Formal writing	The system in which this occurs…
By which	Method, means, agency	Technical/legal writing	The method by which results were obtained…
Wherein	Embedded location (archaic/formal)	Contracts, law	The clause wherein terms are agreed…
Where	Informal place/time	Everyday writing	The place where he grew up…

Writing Tips for Clear, Confident Usage

• Read the sentence aloud- does it sound natural?
• Ask yourself what the clause is explaining: Where? How? Why?
• Choose formality based on your reader.
• Avoid awkward split prepositions–“The method the data was collected” → clunky.

Practice Section: Try It Yourself

Fill in the blanks with “by which” vs “in which”.

• The committee reviewed the process by which the funds were distributed.
• This is the case where the system failed.
• The channel through which these messages were delivered was compromised.
• They analyzed the environment in which the bacteria thrived.

Answers:

• by which
• in which
• by which
• in which

Summary: What You Need to Remember

• “By which” = means/method/agency
• “In which” = condition/location/time
• “Wherein” = old-school “in which” for ultra-formal use
• “Where” = conversational, simple, everyday usage

Choosing between them isn’t about sounding smart- it’s about being clear.

Additional Grammar Insights You’ll Love

• One of the Best or One of the Bests?
• Weaved or Woven – Which Is Correct?
• On the Same Page – 10 Alternatives for Team Communication
• Grammarly’s Guide to Prepositions

Final Thoughts

Mastering the use of “by which” vs “in which” isn’t just a grammar flex- it’s about precision, clarity, and professionalism. Whether you’re crafting legal contracts, research papers, business emails, or formal reports, knowing the difference can elevate your communication.

Here’s the golden rule:
👉 Use “by which” to explain how something happens.
👉 Use “in which” to describe where or when something occurs.

They may seem interchangeable at first glance, but their functions are worlds apart. By applying these distinctions thoughtfully, you’ll avoid ambiguity and sound like a confident, capable communicator.

Keep revisiting examples, read high-quality writing, and most of all-practice. The more you write with these tools in mind, the more naturally they’ll flow into your speech and writing.

FAQs

What is the main difference between “by which” vs “in which”?

The main difference lies in function:

• “By which” explains the method or means (e.g., the process by which data is analyzed).
• “In which” describes a place, time, or condition (e.g., the situation in which he succeeded).

Each serves a distinct grammatical role and should be used accordingly.

Can I use “where” instead of “in which”?

Yes-but only in informal or semi-formal contexts.
While “where” often sounds more natural in casual writing or conversation (the house where I grew up), “in which” is better suited for formal or technical documents where precision is important.

Is “wherein” still used today?

Yes, but rarely-and mostly in legal, academic, or historical contexts.
For instance, the clause wherein the rights are outlined.
Unless you’re aiming for a very formal tone, it’s safer (and clearer) to use “in which.”

Can “by which” vs “in which” be used in the same sentence?

Absolutely, and it often results in highly structured, formal writing.
Example: The framework by which the policy is enforced and the context in which it was created are both critical to understanding its impact.

Just ensure each phrase modifies the appropriate noun and doesn’t create confusion.

How can I remember when to use each phrase?

Try this quick memory trick:

• Think “B” in “by” = Blueprint → the method something is done.
• Think “I” in “in” = Inside → the environment, place, or time something happens.

This simple association helps anchor the phrase’s meaning without overthinking it.