When it comes to English grammar, some phrases appear deceptively similar but carry different shades of meaning. “By which” and “In which” are classic examples that confuse learners, writers, and even native speakers. The difference lies in precision, context, and grammatical function. If you’ve ever paused mid-sentence wondering which one to use, you’re not alone.
This guide breaks it down with clarity, real-life examples, and tables so you can master both forms with confidence.
Understanding the Core Difference Between By Which and In Which
At its heart, the distinction lies in relationship and circumstance:
- By which → points to the means, method, or cause.
- In which → points to the situation, setting, or container (literal or abstract).
Think of it this way:
| Phrase | Core Meaning | Example | Context |
| By which | Refers to method, process, or means | The method by which the data was encrypted is secure. | Process / cause |
| In which | Refers to place, situation, or circumstance | The room in which the meeting was held was small. | Space / situation |
👉 Quick tip: If you can replace it with “the method” or “the means”, use by which. If you can replace it with “the place” or “the situation”, use in which.
Quick Grammar Table: Comparing Meanings, Roles, and Functions
| Aspect | By Which | In Which |
| Function | Indicates method, cause, or process | Indicates container, situation, or state |
| Relative Pronoun Role | Modifies verbs and processes | Modifies nouns related to places or contexts |
| Synonyms | through which, via which | where, wherein |
| Formal Usage | Academic, technical, contracts | Narrative, descriptive, everyday speech |
| Example | The system by which votes were counted was transparent. | The conference in which industry leaders met was in Toronto. |
The Role of Prepositions in English Grammar
Both phrases combine a preposition + relative pronoun (which).
- Prepositions connect the noun to the verb, adjective, or adverb.
- “Which” acts as a relative pronoun that ties the clause back to a subject.
Example Breakdown
- The formula by which the result was derived is complex.
- “By” → shows the method.
- “Which” → refers back to “formula.”
- “By” → shows the method.
- The city in which she was born is beautiful.
- “In” → shows location.
- “Which” → refers back to “city.”
- “In” → shows location.
Why Learners Find By Which vs In Which Challenging
The challenge arises because:
- Both phrases appear in formal English.
- In casual conversation, people often replace them with simpler forms:
- “the way that” instead of by which
- “where” instead of in which
- “the way that” instead of by which
| Formal | Casual Replacement |
| The means by which he succeeded was hard work. | The way he succeeded was hard work. |
| The neighborhood in which I grew up is quiet. | The neighborhood where I grew up is quiet. |
👉 Learners often ask: “Is it wrong to use where instead of in which?” The answer: not wrong in speech, but in academic, legal, or professional contexts, in which is more precise.
Precision and Clarity: Choosing the Right Expression
When you’re drafting an essay, legal contract, or research paper, precision matters.
- By which emphasizes how something happens.
- In which emphasizes the setting in which it happens.
Example (Legal Context):
- The contract outlines the process by which disputes are settled through arbitration.
- The clause in which the responsibilities are defined is binding.
👉 In both cases, clarity avoids ambiguity, misinterpretation, or disputes.
Sentence Construction: Where to Use By Which
Use by which when the subject is about:
- Method
- Means
- Mechanism
- Process
Examples
- The system by which votes were counted was transparent.
- The natural selection process by which species evolve is fascinating.
- The algorithm by which the program operates is efficient.
Quick Table
| Usage | Correct Sentence |
| Science | The process by which water is purified is called filtration. |
| Technology | The encryption method by which data is secured is advanced. |
| Law | The statute by which the defendant was judged is outdated. |
Sentence Construction: Where to Use In Which
Use in which when referring to:
- Place
- Setting
- Situation
- Container (literal or abstract)
Examples
- The room in which the valuables were kept was locked.
- The scenario in which she found herself was unexpected.
- The conference in which leaders gathered was in New York.
Quick Table
| Usage | Correct Sentence |
| Location | The museum in which the painting was displayed is famous. |
| Situation | The circumstances in which the contract was signed were unclear. |
| Storytelling | The dream in which Anna was flying felt real. |
Real-Life Scenarios: Speaking vs Writing
- In speaking → we prefer shorter, casual alternatives:
- “the way” for by which
- “where” for in which
- “the way” for by which
- In writing → especially academic, legal, or professional, the formal forms are required.
Examples:
- Spoken: That’s the way he solved it.
- Written: That’s the method by which he solved it.
- Spoken: The place where we met was cozy.
- Written: The place in which we met was cozy.
Relative Clauses Explained with Examples
Both phrases are relative clauses. They give extra information without starting a new sentence.
- Restrictive clause (essential meaning):
- The method by which vaccines are developed has changed.
- The method by which vaccines are developed has changed.
- Non-restrictive clause (additional detail):
- Toronto, in which the event was held, is a major hub for conferences.
- Toronto, in which the event was held, is a major hub for conferences.
👉 Comma usage matters:
- With commas → extra info.
- Without commas → essential info.
Formal vs Informal Usage in Modern Communication
| Register | By Which | In Which |
| Formal Writing | Research papers, contracts, laws | Policies, reports, narratives |
| Informal Writing / Speech | Rare, replaced by “the way” | Often replaced by “where” |
| Emails | The method by which data is shared… | The folder in which the files are stored… |
| Casual Talk | That’s how… | That’s where… |
👉 In 2025, trends in modern English show casual forms dominating social media, forums, and conversation, while formal structures remain standard in law, academia, and contracts.
Examples from Literature, Movies, and Everyday Conversation
- Literature: The novel describes the journey in which the hero discovers himself.
- Movies: In Black Swan (starring Natalie Portman, Academy Award winner), the plot is a world in which art and obsession collide.
- Everyday Speech: The game by which they judged the winner was unfair.
FAQs
Q1: Is it correct to use “where” instead of “in which”?
Yes, in informal contexts. But in academic or legal writing, in which is more precise.
Q2: Can “by which” and “in which” be interchangeable?
Not usually. By which shows method; in which shows situation/place.
Q3: Which phrase is more common in modern English?
“In which” is more common in speech, while “by which” dominates academic writing.
Q4: How do I avoid mistakes with these phrases?
Ask: Does it describe a method (by which) or a situation/place (in which)?
Q5: Are there synonyms for these phrases?
Yes. By which = “through which,” “via which.”
In which = “where,” “wherein.”
Conclusion: Mastering the Nuances of By Which vs In Which
Mastery comes from practice, not memorization. Think in terms of method vs situation:
- If it’s about how something happens, use by which.
- If it’s about where or in what situation something happens, use in which.
Whether you’re drafting a research paper, legal contract, or a simple narrative, choosing the right phrase adds clarity, precision, and authority to your writing.
