“By which” and “in which” both introduce relative clauses, but they work with different verbs and express different relationships. “By which” describes the method or means of doing something, connecting to verbs that need “by” (like “achieved by” or “caused by”), while “in which” describes location, context, or circumstances, connecting to verbs that need “in” (like “occurred in” or “lived in”). For example, “This is the method by which we solved the problem” uses “by” to show how something was done, whereas “This is the town in which I grew up” uses “in” to show where something happened.
The choice depends entirely on what preposition the verb in your sentence requires—if you’d normally say “by” with that verb, use “by which”; if you’d say “in” with that verb, use “in which”. You can’t swap them freely because each preposition creates a different meaning. Learning which verbs pair with which prepositions helps you choose correctly every time.
By Which or In Which: What’s the Difference?
The main difference lies in the type of relationship each preposition expresses. “By” shows method, means, or agency—how something happens. “In” shows location, context, or circumstances—where or when something happens.
When you use “by which,” you’re explaining how, through what method, or by what means something occurs. The verb in your sentence needs “by” to make sense. For instance, “achieved by,” “caused by,” or “made by.”
When you use “in which,” you’re describing where something happens, what situation contains it, or what context surrounds it. The verb needs “in” to work properly. Examples include “occurred in,” “lived in,” or “happened in.”
The preposition you choose must match the verb you’re using. You can’t just pick one randomly—the verb dictates which preposition works.
When Do You Use ‘By Which’?
Use “by which” when the verb in your sentence needs “by” to express method, means, or agency.
Common verb phrases that need “by”:
- Achieved by, accomplished by, reached by
- Caused by, created by, made by
- Measured by, judged by, evaluated by
“This is the process by which we manufacture the product” works because you’d say “manufacture by a process.” The verb “manufacture” pairs with “by” when describing method.
“The criteria by which we judge performance include accuracy and speed” uses “by” because you “judge by criteria.”
In academic writing, “by which” appears often when describing research methods. When editing scholarly papers, I notice writers struggle with this when explaining procedures.
When Should You Use ‘In Which’?
Use “in which” when the verb needs “in” to show location, time, context, or circumstances.
Common verb phrases that need “in”:
- Occurred in, happened in, took place in
- Lived in, worked in, studied in
- Found in, located in, situated in
“This is the building in which the meeting will take place” works because you’d say “take place in a building.” The verb “take place” pairs with “in” for location.
“The year in which we launched the product was 2020” uses “in” because events happen “in” a year.
“In which” also describes situations: “The circumstances in which we made the decision were difficult.” You’d say the decision was made “in circumstances,” so “in which” fits.
How Do Prepositions Change Meaning?
Swapping “by” and “in” changes the sentence’s meaning completely. The preposition tells readers what relationship you’re describing.
Compare these:
- “The method by which we travel is train.” (How we travel)
- “The country in which we travel is France.” (Where we travel)
Same structure, different prepositions, different meanings. “By which” answers “how?” while “in which” answers “where?”
The verb determines which preposition you need. Test without the relative clause:
- “We travel by train” → “The method by which we travel”
- “We travel in France” → “The country in which we travel”
When editing technical documents, I see writers mix these up when they forget to check what the base verb requires.
Examples Showing Both Phrases
Correct Usage Examples
“The tool by which we measure success is customer satisfaction.”
This uses “by” because you “measure by” a tool.
“The city in which the conference takes place is Chicago.”
This needs “in” because events “take place in” locations.
“The procedure by which doctors diagnose the condition involves blood tests.”
You “diagnose by” a procedure, so “by which” works.
“The situation in which we found ourselves was unexpected.”
You “find yourself in” a situation, not “by” a situation.
“The means by which she achieved her goals included hard work.”
You “achieve by means,” making “by which” correct.
“The building in which our office is located was built in 1920.”
Your office is “located in” a building, so “in which” fits.
Incorrect Usage Examples
- Incorrect: “The method in which we solved it was effective.”
- Correct: “The method by which we solved it was effective.”
Why: You solve problems “by” a method, not “in” a method.
- Incorrect: “The town by which I grew up is small.”
- Correct: “The town in which I grew up is small.”
Why: You grow up “in” a place, not “by” a place.
- Incorrect: “The process in which the product is made is complex.”
- Correct: “The process by which the product is made is complex.”
Why: Products are made “by” a process. Method needs “by.”
- Incorrect: “The year by which this happened was 2015.”
- Correct: “The year in which this happened was 2015.”
Why: Events happen “in” a year, not “by” a year.
Context Variations
Academic writing uses both: “The methodology by which data was collected” and “The context in which the study occurred.” Precision matters in scholarly work.
Technical documentation favors “by which” for procedures: “The algorithm by which the software processes requests.” Process descriptions need method language.
Legal documents use “in which” for circumstances: “The conditions in which the contract was signed.” Context and situation get “in.”
Business reports mix both: “The strategy by which we entered the market” (method) versus “The quarter in which sales peaked” (time).
Common Mistakes with Relative Clauses
| Mistake | Example | Why It’s Wrong | Correction |
| Wrong preposition for verb | “The way in which we travel is bus” | Travel “by” bus, not “in” bus | “The way by which we travel is bus” |
| Mixing location and method | “The city by which the event occurs” | Events occur “in” places | “The city in which the event occurs” |
| Using “by” for time | “The day by which it happened” | Time uses “in” | “The day in which it happened” |
| Using “in” for means | “The tool in which we fixed it” | Fix “by” a tool | “The tool by which we fixed it” |
| Omitting preposition entirely | “The method which we used” | Needs preposition | “The method by which we used” |
These errors happen when writers don’t check what preposition the verb needs. The relative clause structure makes it less obvious, but the same rules apply.
Across student papers, I notice this mistake appears most when students translate directly from languages that don’t use prepositions the same way English does. The solution is always testing the sentence without “which” first.
Memory Tricks for Choosing Correctly
Ask yourself: “What preposition does this verb need?” Remove the relative clause and make a simple sentence. If you’d use “by” in the simple version, use “by which.” If you’d use “in,” use “in which.”
Remember: BY = HOW (method, means). IN = WHERE or WHEN (location, time, context).
Test sentence: “We achieved success _____ hard work.” You’d say “by hard work,” so write “The means by which we achieved success was hard work.”
Think about common pairs:
- Method BY which, process BY which, means BY which (all about HOW)
- Place IN which, time IN which, situation IN which (all about WHERE/WHEN)
Create a simple version first, then build the relative clause. “We lived in Boston” becomes “The city in which we lived was Boston.” “We succeeded by teamwork” becomes “The method by which we succeeded was teamwork.”
Conclusion
Choosing between “by which” and “in which” depends on what preposition your verb needs—”by” for method and means, “in” for location and context. This isn’t about style or preference; it’s about grammatical accuracy based on verb-preposition relationships.
The best approach is testing your sentence without the relative clause to see which preposition fits naturally. Once you know whether you’d say “achieved by” or “occurred in” for your specific verb, you know whether to use “by which” or “in which.”
This skill improves both your writing precision and your ability to construct clear, grammatically correct relative clauses.
Frequently Asked Questions
“By which” shows method or means (how), while “in which” shows location, time, or context (where/when).
No. The verb in your sentence determines which preposition you need. They create different meanings.
Use it when the verb needs “by”—for example, “achieved by,” “caused by,” or “measured by.”
Use it when the verb needs “in”—for example, “occurred in,” “lived in,” or “found in.”
Often yes. “The place in which I work” means the same as “The place where I work.” “Where” is simpler.
Both work but mean different things. “The way in which” describes circumstances. “The way by which” describes method.
Verbs showing method, creation, or measurement: achieve, accomplish, make, create, measure, judge, evaluate, cause.
Verbs showing location, occurrence, or context: happen, occur, live, work, take place, find, locate, result.
