English can be tricky, especially when it comes to prepositional phrases like “by which” and “in which.” These little phrases may seem harmless, but using them incorrectly can make your writing sound awkward—or worse, completely change the meaning of a sentence.
Imagine you’re writing an important email, and you hesitate: “Is it ‘the process by which’ or ‘the process in which’?” You second-guess yourself, maybe even rephrase the whole thing to avoid the confusion. Sound familiar? Don’t worry—you’re not alone!
In this guide, we’re breaking down everything you need to know about these two phrases. What do they mean? How do you use them correctly? Are there better alternatives? We’ll answer all of these questions and more—using simple explanations, real-world examples, and a friendly, conversational tone.
So, if you’ve ever found yourself stuck wondering whether to use “by which” or “in which,” this article is for you. Get ready for some grammar clarity!
The Core Difference Between “By Which” and “In Which”
Let’s start with the biggest distinction between these two phrases. It all comes down to what they express:
- “By Which” refers to a method, means, or agent—basically, how something happens.
- “In Which” refers to a place, time, or situation—essentially, where or when something happens.
Think of it this way:
- “By which” = how something happens.
- “In which” = where or when something happens.
For example:
- “This is the rule by which we operate.” (Means: We follow this rule.)
- “This is the year in which everything changed.” (Time: This happened during this year.)
See the difference? Let’s break it down further.
“By Which” Explained With Real-Life Examples
“By which” helps explain the method, means, or process through which something happens. It often replaces “by it” or “through it.”
Think of it as answering the question: How?
- “The method by which they built the pyramids is still debated.” (How did they build them?)
- “She discovered the law by which gravity works.” (How does gravity work?)
It’s also common in formal or academic writing, especially when explaining rules or principles.
- “That is the standard by which all candidates are judged.”
- “There’s a system by which information is transferred.”
If you’re explaining a cause-and-effect relationship or a process, “by which” is your best choice.
“In Which” Explained With Simple Examples
“In which” is all about location, time, or context. It replaces “in it” and usually follows a noun that refers to a situation, event, or place.
Think of it as answering: Where? When? In what?
- “The meeting in which we discussed the merger was productive.” (Where did we discuss it? In the meeting.)
- “That was the year in which I traveled the world.” (When did I travel? That year.)
It also works for abstract situations:
- “The circumstances in which he left were mysterious.” (What circumstances? The ones he left in.)
- “She was placed in a position in which she had no power.” (What position? One with no power.)
If you’re referring to time, place, or a specific situation, “in which” is your go-to phrase.
Grammar Breakdown: Why These Phrases Matter
Both “by which” and “in which” belong to a category called prepositional relative clauses.
- A relative clause gives more information about a noun.
- A prepositional relative clause starts with a preposition (like “by” or “in”) and connects to “which.”
For example:
- “The law by which we live must be fair.”
- (“By which” connects “law” to “live.”)
- “The situation in which he found himself was strange.”
- (“In which” connects “situation” to “found himself.”)
Understanding this structure helps you use these phrases fluently and naturally.
When to Use “By Which” in Everyday Writing
You’ll most often use “by which” when talking about rules, principles, methods, or explanations.
For example:
- “There’s a process by which water turns to ice.” (Describes how water freezes.)
- “That’s the test by which intelligence is measured.” (Explains how intelligence is judged.)
It also works when describing an agent of action:
- “The method by which he solved the problem was genius.”
- “She found a way by which she could travel for free.”
Anytime you’re explaining “how” something happens, “by which” is your best bet.
When to Use “In Which” in Everyday Writing
Use “in which” when referring to time periods, locations, or abstract situations.
For example:
- “That was the moment in which he realized the truth.” (Refers to time.)
- “She lives in a city in which it rarely snows.” (Refers to location.)
It’s also useful for formal or academic writing:
- “We analyzed the context in which the event took place.”
- “There are conditions in which bacteria thrive.”
Whenever you need to express where or when something happens, “in which” is the way to go.
Common Mistakes and How to Avoid Them
Many people mix these up. Here’s how to avoid the most common errors:
❌ Wrong: “The process in which water turns to ice is interesting.”
✅ Right: “The process by which water turns to ice is interesting.”
❌ Wrong: “That’s the city by which she was born.”
✅ Right: “That’s the city in which she was born.”
A simple trick? If it describes how, use “by which.” If it describes where or when, use “in which.”
Alternatives to “By Which” and “In Which”
Sometimes, these phrases can sound too formal in casual writing. Here are easier alternatives:
- “The way in which” → “How”
- Formal: “The way in which he solved the puzzle amazed me.”
- Casual: “How he solved the puzzle amazed me.”
- “The place in which” → “Where”
- Formal: “This is the town in which I grew up.”
- Casual: “This is the town where I grew up.”
Simplifying makes your writing more natural and conversational.
Quick Cheat Sheet: “By Which” vs. “In Which”
| Phrase | Use When Talking About | Example Sentence |
| By Which | Method, cause, rule | “The rule by which we live is simple.” |
| In Which | Time, place, situation | “The era in which he thrived was the 80s.” |
Keep this table handy to avoid confusion!
Conclusion: Mastering “By Which” and “In Which”
Now, you’ve got a clear understanding of when to use “by which” and “in which.” Just remember:
- “By which” = explains how something happens.
- “In which” = explains where or when something happens.
Grammar can be tricky, but once you understand the patterns, it becomes second nature. So next time you’re stuck choosing between “by which” or “in which,” you’ll know exactly what to do.
FAQs: “By Which” vs. “In Which”
What is the main difference between “by which” and “in which”?
“By which” explains the method, means, or cause of something, while “in which” refers to time, place, or situation.
- By Which: “This is the process by which diamonds are formed.” (How are diamonds formed?)
- In Which: “This is the era in which dinosaurs lived.” (When did dinosaurs live?)
Can I replace “by which” and “in which” with something simpler?
Yes! In casual speech and writing, simpler words often sound better:
- By which → How
- Formal: “The way by which he solved the problem was unique.”
- Casual: “How he solved the problem was unique.”
- Formal: “The way by which he solved the problem was unique.”
- In which → Where/When
- Formal: “The city in which she was born is beautiful.”
- Casual: “The city where she was born is beautiful.”
- Formal: “The city in which she was born is beautiful.”
Is “by which” or “in which” more common in daily conversation?
“In which” is slightly more common because it deals with places and times, which come up a lot in daily speech. “By which” tends to appear in formal, legal, or academic writing where explaining processes is important.
Are “by which” and “in which” always necessary?
Not always! In some cases, you can omit them completely and still have a clear sentence.
- “That’s the rule by which we operate.” → “That’s the rule we operate by.”
- “The year in which I was born was 1995.” → “The year I was born was 1995.”
Can “by which” and “in which” be used interchangeably?
No, because they mean different things. Using the wrong one can confuse your reader.
❌ Incorrect: “The situation by which he was hired was unexpected.”
✅ Correct: “The situation in which he was hired was unexpected.”
(We’re talking about a situation, not a method, so “in which” is correct.)
Do native English speakers use these phrases often?
In spoken English, shorter alternatives (like “where” or “how”) are more common. However, in writing—especially formal writing—”by which” and “in which” are frequently used.
As the visionary founder and CEO of Globals English, Emma Brooke is dedicated to transforming the way individuals learn and master the English language.