When I first started editing a research paper, I remember pausing at a sentence that used “in which” and wondering if “by which” might be more appropriate. That moment taught me how tricky these phrases can be when we’re juggling grammar, tone, and the context of what we’re trying to say. These two expressions, while common, aren’t exactly interchangeable, and knowing their subtle differences can really clarify your writing and avoid unnecessary pitfalls. Whether you’re drafting a formal email, a company policy, or analyzing a filtration process in a science class, your decision on which phrase to use can either make your writing clear or leave it vague, even confusing.
Let’s break this down with real-world examples. “By which” often refers to the method or cause by which something happens — like the process by which water is purified, turning it from impure to pure, from undrinkable to drinkable. “In which,” on the other hand, speaks to the place, situation, or context — the location in which an event unfolds. Think of the whole movement, the function inside a clause, the way one phrase leads to another.
As experienced writers, we know that choosing the correct term isn’t just splitting grammatical hairs — it’s about expressing ideas with precision. Depending on the usage, previous clauses, and what you’re trying to indicate, you must be careful to guide your reader clearly. Even expert tips can be misapplied if you don’t understand the core meanings behind these expressions. For those truly in the writing game, mastering this becomes second nature.
Why Choosing Between ‘By Which’ and ‘In Which’ Matters
Using the wrong prepositional phrase in a sentence can do more than make you sound awkward—it can change your meaning entirely or make your writing unclear. For example:
- ✅ Correct: “The method by which the solution is applied…”
- ❌ Wrong: “The method in which the solution is applied…”
That subtle difference can confuse a reader, especially in academic papers, business memos, or technical writing. And if you’re a student, teacher, or professional in the USA, clear grammar isn’t optional—it’s expected.
Understanding the Core Grammar: Relative Clauses & Prepositional Phrases
To understand in which and by which, you first need to understand two grammar concepts:
Relative Clauses
A relative clause gives extra information about a noun and usually starts with a relative pronoun like which, that, who, or whose.
- “This is the law which governs the system.”
Prepositional Phrases
These phrases combine a preposition (like in, by, on, to, etc.) with a relative pronoun to describe how something is done, where it’s located, or what it refers to.
- “The agreement in which the terms were outlined…”
- “The system by which we measure progress…”
When these come together, they form powerful, precise sentences—but only when used correctly.
What Does ‘In Which’ Mean and When Should You Use It?
“In which” is used to describe a situation, context, or environment where something occurs. It’s usually more formal than saying “where.”
Use In Which When:
- You are describing a setting, context, or abstract location.
- You’re writing or speaking in a formal or academic tone.
- “Where” would be too informal or imprecise.
Examples of “In Which”
| Context | Example Sentence |
| Academic | “The study highlights scenarios in which learning improves.” |
| Business | “They signed a deal in which both parties benefit.” |
| Legal/Policy | “The law outlines the circumstances in which penalties apply.” |
Real-Life Example:
A U.S. government report states:
“There are multiple frameworks in which economic growth can be measured.”
— U.S. Department of Commerce
Quick Tip:
If you’re replacing where in formal writing, try in which. But if it sounds clunky or unclear, restructure the sentence entirely.
What Does ‘By Which’ Mean and When Should You Use It?
“By which” refers to the means, method, or process through which something is done. It often answers the question: how?
Use By Which When:
- You’re describing how something happens.
- You’re dealing with mechanisms, methods, or systems.
- You need to sound precise, especially in technical or professional writing.
Examples of “By Which”
| Context | Example Sentence |
| Scientific | “Photosynthesis is the process by which plants produce energy.” |
| Academic | “The method by which the samples were collected is flawed.” |
| Business/Tech | “This is the system by which we track user engagement.” |
Real-Life Example:
From a research article on machine learning:
“The algorithm defines the logic by which patterns are identified.”
Quick Tip:
You can often substitute by which with through which or via which—this is a good test to make sure you’re using it properly.
When to Use ‘Where’ Instead of ‘In Which’
Sometimes “in which” sounds too stiff, especially in spoken or informal writing. That’s where “where” comes in.
Use Where When:
- The sentence sounds too clunky with “in which.”
- You’re writing casually or for easier readability.
- You’re describing a literal place rather than an abstract one.
Example Swap:
- Formal: “The university in which I studied…”
- Natural: “The university where I studied…”
But don’t get lazy—where isn’t always right, especially when writing academic essays, legal documents, or research papers.
Is ‘Wherein’ Still Used? Or Just Outdated?
“Wherein” is an older, more formal way to say in which. While less common in everyday use, it still appears in:
- Legal writing
- Research publications
- Contracts and policies
- Religious or historical texts
Example:
“This contract outlines the conditions wherein both parties agree to binding arbitration.”
Warning:
Avoid using “wherein” unless you’re deliberately writing in a highly formal tone or following legal or scholarly conventions.
Common Mistakes to Avoid With ‘By Which’ and ‘In Which’
Even native speakers mix these up. Here’s what to watch out for:
Mistake 1: Mixing Up Method vs. Location
- Wrong: “The book by which he found answers…”
- Right: “The book in which he found answers…”
Mistake 2: Using ‘Where’ Too Casually
- Wrong (in an academic paper): “The scenario where interest grows…”
- Right: “The scenario in which interest grows…”
Mistake 3: Adding Redundant Prepositions
- Wrong: “The system in which that it works…”
- Right: “The system in which it works…”
Comparing ‘By Which’ vs ‘In Which’ Side-by-Side
Here’s a simple breakdown to help you visually decide when to use each phrase:
| Phrase | Meaning | Used For | Sample Sentence |
| In Which | Context, setting, condition | Formal situations, academic writing | “The case in which the rules changed…” |
| By Which | Method, means | Explaining how something works | “The method by which it is done…” |
| Where | Literal place | Casual writing, conversations | “The room where it happened…” |
| Wherein | Formal version of ‘in which’ | Legal or historical usage | “The document wherein the rights are granted…” |
Choosing the Right Phrase in Academic, Business, and Legal Contexts
When you’re writing for a professional or educational audience, word choice matters. Here’s how each phrase fits into common writing scenarios in the U.S.
Academic Writing
- Use in which for structured essays and research.
- Use by which when describing methods or results.
Business Writing
- Use by which for describing systems or workflows.
- Use in which for reports or strategic descriptions.
Legal/Policy Writing
- Use wherein only when legal tone is required.
- Use in which for clauses or terms.
- Avoid where unless the tone allows.
Tips to Improve Grammar Clarity in Professional Writing
Want to sound sharp and credible? Follow these simple habits:
Editing Tips
- Read aloud to catch awkward phrasing.
- Use grammar tools like Grammarly or Hemingway Editor.
- Replace where with in which when precision is needed.
- Ask: Am I describing a method (by which) or a setting (in which)?
Checklist Before Finalizing Your Sentence:
- Does it describe how something happens? → Use by which
- Does it describe where or under what condition something happens? → Use in which
- Is the tone casual or formal?
- Would a clearer sentence structure work better?
Summary Table: Quick Reference for Grammar Use
| Expression | Meaning | Tone | Use When… | Example |
| In Which | Location/context | Formal | Describing a place, condition, or scenario | “The room in which the painting hung…” |
| By Which | Method/process | Formal | Explaining how something is done | “The process by which they analyze data…” |
| Where | Literal place | Neutral | In casual or conversational writing | “The place where we met was packed.” |
| Wherein | Legal/formal | Very Formal | Legal contracts or historical documents | “The clause wherein the party agrees…” |
Conclusion
Choosing between “by which” and “in which” may seem like a small detail, but it can make a big difference in how your message is received. These phrases are often misunderstood or used interchangeably, leading to unclear writing or even the opposite of what you meant. The key is knowing the function each plays in a sentence:
one describes the method or process (by which), the other describes the context or location (in which). Whether you’re writing a research paper, formal email, or just trying to be more precise in your everyday writing, understanding this difference will help you express your thoughts more clearly and professionally. Like all great writing habits, it takes awareness, some practice, and a willingness to revise. But once you master it, choosing the right phrase becomes second nature.
FAQs
1. What is the main difference between “by which” and “in which”?
“By which” refers to the method, cause, or process through which something happens.
“In which” refers to the place, context, or situation where something happens.
2. Can I use “by which” and “in which” interchangeably?
No. They have different meanings and functions. Using one in place of the other can change the message entirely or make your sentence confusing or incorrect.
3. Is it better to avoid using these phrases altogether?
Not necessarily. When used correctly, they add clarity and precision to your writing. The goal is not to avoid them, but to use them correctly based on context.
4. Where are these phrases most commonly used?
They are often found in academic writing, formal emails, company policies, and anywhere precise sentence structure and tone matter.
5. How can I get better at using these phrases?
Read carefully written texts, note how these phrases are used, and practice rewriting your own sentences with them. Over time, this will help you visualize and apply them more naturally.
