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

When I’ve paused mid-sentence, feeling unsure whether to use “by which” or “in which,” I realize many experienced writers face the same challenge. These formal-sounding phrases often trip people up because their core meanings and function vary depending on contexts. Choosing the right phrase should become second nature, though it isn’t always easy. This guide aims to clarify the precise definitions and subtle differences in tone, grammar, and usage. You’ll find real-world examples, expert tips, and a reference table to help avoid common pitfalls that create a confusing mix.

Splitting grammatical hairs over “by which or in which” really matters, especially because using the wrong phrase in writing – whether in a research paper, formal email, or company policy – can make your sentence vague, confusing, or outright incorrect. For example, saying “the situation by which we made the decision was chaotic” is wrong; the correct form is “the situation in which we made the decision was chaotic.” These phrases don’t mean the same thing and are not interchangeable. If you break it down, “by which” often refers to a cause or method, while “in which” refers to a place or context. Understanding this difference will help you save yourself from mixing them again and keep you at the bottom of your writing game.

Understanding the Key Difference Between “By Which” and “In Which”

Here’s the golden rule:

• If you’re explaining how something happens → use by which.
• If you’re explaining where or when something happens (often abstract) → use in which.

How to Use “In Which” Properly

The phrase “in which” is a preposition-pronoun combo used to add clarity and precision when referring to non-physical places, situations, or points in time.

Common contexts:

• Abstract locations: situation, case, context, scenario, example, instance
• Formal writing: academic papers, legal writing, reports

Examples:

• ✅ “The moment in which she realized her mistake was pivotal.”
• ✅ “The case in which the defendant was found guilty set a precedent.”
• ✅ “The scenario in which both teams tie is unlikely.”

Tip:

Avoid using “where” when referring to abstract concepts in formal writing. “Where” works for physical locations, but sounds awkward or incorrect when used in place of “in which” in non-physical situations.

❌ “The case where he was acquitted…” ✅ “The case in which he was acquitted…”

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

“By which” is typically used to describe the means, process, or method by which something occurs. It often replaces longer expressions like “through which”, “by means of which”, or “via which”.

Common contexts:

• Legal procedures
• Scientific methods
• Technical manuals
• Historical accounts

Examples:

• ✅ “The legal process by which laws are enacted is complex.”
• ✅ “The technology by which data is encrypted has evolved rapidly.”
• ✅ “The criteria by which applications are judged must be transparent.”

This phrase emphasizes cause, mechanism, or agency – so it’s ideal when you’re talking about how something happens.

Avoiding Common Mistakes: By Which vs In Which

Even native speakers mix them up – especially in formal writing. Here are the most frequent errors and how to fix them.

Mistake 1: Swapping them interchangeably

❌ “The clause by which disputes are handled is vague.” ✅ “The clause in which disputes are handled is vague.”

→ Why? You’re referring to the location (a clause), not the means.

Mistake 2: Overusing them in casual writing

Sometimes, simple wording is better.

❌ “That’s the process by which we prepare coffee.” ✅ “That’s how we make coffee.”

→ If the tone is informal, ditch the formality.

Mistake 3: Using “where” in place of “in which” improperly

❌ “The case where he was proven guilty…” ✅ “The case in which he was proven guilty…”

→ Use “where” only for physical spaces unless writing informally.

Sentence Surgery: Real Examples Fixed and Explained

Let’s look at flawed examples pulled from real-world forums, and clean them up:

❌ Incorrect:

“The way where we arrived at the solution was unorthodox.”

✅ Correct:

“The way by which we arrived at the solution was unorthodox.”

❌ Incorrect:

“The story by which he told shocked everyone.”

✅ Correct:

“The story in which he told the truth shocked everyone.”

🔍 Why? You’re referring to the context or content of the story, not the means.

Formality, Clarity, and Context: Why Precision Matters

Using these phrases correctly doesn’t just improve grammar – it elevates your writing.

Where it really matters:

• Academic theses
• Legal documents
• Government reports
• Scientific studies

You’ll often see:

• “The method by which”
• “The circumstances in which”
• “The law by which”
• “The event in which”

This usage brings precision and removes ambiguity – especially where misinterpretation can have serious consequences.

By Which or In Which: Quick Decision Guide

Here’s a fast reference guide to help choose the correct expression:

Mini Quiz: Can You Spot the Right Phrase?

Choose the correct option:

1. The contract outlines a clause ___ disputes must be settled in arbitration.
   • A. by which
   • B. in which ✅ Answer: B. in which
2. The process ___ water is purified involves several stages.
   • A. in which
   • B. by which ✅ Answer: B. by which
3. The moment ___ everything changed was unforgettable.
   • A. by which
   • B. in which ✅ Answer: B. in which
4. The method ___ the vaccine was developed is revolutionary.
   • A. in which
   • B. by which ✅ Answer: B. by which

Case Study: Legal vs Technical Writing

Legal Writing Example

“The statute by which the agency was formed outlines specific responsibilities.”

Here, “by which” explains how the agency came into existence – perfect use in a legal context.

Technical Writing Example

“We described the environment in which the experiment was conducted.”

Here, the emphasis is on the setting or context of the experiment – making “in which” the right choice.

Writing Tip:

When in doubt, reword the sentence using “how” or “where.” If “how” fits, use by which. If “where” or “when” fits (formally), use in which.

Expert Insights: What Editors and Linguists Say

✍️ “Precision in grammar isn’t about rules for rules’ sake. It’s about conveying your meaning exactly as you intended.”   –  Dr. Karen Adams, Professor of Linguistics, Stanford University

✍️ “’By which’ and ‘in which’ are markers of careful thinking. Their proper use shows respect for both language and reader.”   –  Linda McLain, Senior Legal Editor

By Which or In Which? Cheat Sheet Summary

Final Thoughts

If you’ve ever hesitated over “by which or in which,” now you’ve got the clarity – and tools – to choose correctly. Just remember:

• Think function: method vs context.
• Use formality as a guide.
• Replace the phrase with how or where to test it.
• Don’t overuse either – natural flow matters.

The right phrase won’t just be grammatically correct – it will be clear, precise, and professional.

FAQs

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

“By which” is used to describe the method or means through which something happens, while “in which” refers to the context, time, or setting where something occurs. Think of “by which” as answering how, and “in which” as answering where or when (especially in formal or abstract contexts).

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

No, they are not interchangeable. Using the wrong one can change the meaning of a sentence or make it grammatically incorrect. Always assess whether you’re describing a method (by which) or a setting/context (in which) before choosing.

Is “where” the same as “in which”?

Not exactly. While “where” can sometimes replace “in which” in informal writing, it is best to use “in which” in formal or academic contexts – especially when referring to abstract situations, legal cases, or non-physical settings. For example: “The situation in which they found themselves… “The situation where they found themselves…”

How can I test if I’m using “by which” correctly?

Try replacing “by which” with “how” or “by means of which.” If the sentence still makes sense, your usage is probably correct. “The system by which votes are counted…” → “The system by means of which votes are counted…”

Why is this distinction important in professional writing?

In business, law, academia, and technical writing, clarity and precision are essential. Choosing the right phrase – “by which” for mechanisms, “in which

Emma Clark