By which or in which are small phrases that often cause big questions about prepositions, relative clauses, and precise meaning. In many sentences a writer must choose between by which (preposition by + relative pronoun which) and in which (preposition in + relative pronoun which) to show correct relation, direction, or method.
Consider the example “the method by which we measure” where the is an article, method is a noun, by is a preposition, which is a relative pronoun, we is a pronoun, measure is a verb, and the clause shows method as the means. Or compare “the room in which we met” where in clearly marks location and met is the past tense verb that agrees with subject we.
Throughout this article I identify parts of speech, check verb tenses and subject–verb agreement, review article and preposition choices for precision, and revise sentences to remove fragments and run-ons. Examples will show how meaning changes when you choose by which versus in which, and practical tips will help you pick the correct phrase for formal writing, speech, and editing.
Read on for contextual examples, common mistakes, American vs British differences, idiomatic uses, practical tips, a short conclusion, and a ten-item FAQs section.
Contextual Examples
Location Versus Means
Example 1 (location): “the room in which the meeting took place.”
- Parts of speech: the (definite article), room (noun), in (preposition), which (relative pronoun), the (article), meeting (noun), took (verb, past tense), place (noun).
- Verb check: took is past tense and agrees with the singular noun meeting as its subject within the clause; the clause is the meeting took place, a complete clause introduced by which.
- Meaning: in which marks the location where the meeting happened.
Example 2 (means): “the method by which we collect data.”
- Parts of speech: the (article), method (noun), by (preposition), which (relative pronoun), we (pronoun), collect (verb, present tense), data (noun).
- Verb check: collect is present tense and agrees with plural subject we. If narrating the past, use collected.
- Meaning: by which indicates the means or instrument used to collect data.
Agent or Instrument (Passive Constructions)
Example 3 (agent in passive): “a law by which people are protected.”
- Parts of speech: a (indefinite article), law (noun), by (preposition), which (relative pronoun), people (noun), are (verb, present tense plural), protected (past participle used in passive).
- Verb check: are protected is passive voice in the present tense and agrees with plural noun people. If the subject were singular (the person is protected).
- Meaning: by which introduces the agent or instrument that achieves protection, often used with passive voice.
Time Reference
Example 4 (time and place): “the year in which she graduated”
- Parts of speech: the (article), year (noun), in (preposition), which (relative pronoun), she (pronoun), graduated (verb, past tense).
- Verb check: graduated is past tense and agrees with singular subject she.
- Meaning: in which marks time; the year contains the event.
Cause or Reason (Careful Choice)
Example 5 (reason): “the reason by which this error occurred” — awkward.
- Revision: “the reason for which this error occurred” or better “the reason why this error occurred.”
- Analysis: for which or why better mark cause than by which; by which suggests method, not cause.
Method and Procedure
Example 6 (procedural step): “the step by which the solution is achieved” — acceptable in technical contexts.
- Parts of speech: the (article), step (noun), by (preposition), which (relative pronoun), the (article), solution (noun), is achieved (passive verb phrase).
- Verb check: is achieved is present passive and agrees with singular subject solution.
Common Mistakes
Mistake 1: Mixing Location and Means
Error: “the box by which the toys were inside.”
- Problems: by which incorrectly used with an inside relation; the phrase is awkward and semantically wrong.
- Correction: “the box in which the toys were placed” or “the box in which the toys were kept.”
- Parts-of-speech check: the (article), box (noun), in (preposition), which (relative pronoun), the (article), toys (noun plural), were placed (verb phrase, past passive); were agrees with plural toys.
Mistake 2: Using By Which for Cause
Error: “the reason by which he resigned.”
- Why it fails: by which implies method, not cause.
- Better: “the reason why he resigned” or “the reason for which he resigned.”
- Parts-of-speech check: reason (noun), why (conjunction/relative adverb), he (pronoun), resigned (verb, past tense) — verb tense and agreement are correct.
Mistake 3: Redundant Prepositions
Error: “the way by in which we…”
- Correction: Remove redundancy: “the way in which we…” or “the way by which we…” depending on intended meaning.
- Tip: Keep only the preposition that matches the intended relation: in (location/containment/time), by (means/agent), with (instrument or accompaniment).
Mistake 4: Tense Mismatch in Relative Clause
Error: “the method by which we collected data is working” (tense mismatch may confuse timeline).
- Correction: Keep tenses consistent or clearly signal sequence: “the method by which we collected data was effective” (both past), or “the method by which we collect data is effective” (both present).
- Parts-of-speech: method (noun), by (preposition), which (relative pronoun), we (pronoun), collected/collect (verb), data (noun), is/was (verb).
Mistake 5: Dangling Relative or Fragment
Error fragment: “By which we measured.” alone lacks a clear noun antecedent.
- Correction: Attach clause properly: “The tool by which we measured was calibrated.”
- Parts-of-speech: the (article), tool (noun), by (preposition), which (relative pronoun), we (pronoun), measured (verb).
American vs British English Differences
Usage Is Largely Shared
Both American and British English use by which and in which with the same core differences: in which marks location or time, by which marks means, agent, or instrument. Style choices and register are similar across the varieties.
Formality and Preposition Stranding
- Formal written English often places the preposition before which: “the city in which I live.” This is common in both American and British formal writing.
- Informal speech and American colloquial writing often use preposition stranding with that/which or omit which: “the city I live in.” Both varieties accept stranded prepositions in less formal contexts, though rephrasing avoids ending with a preposition in very formal documents.
Example (formal, British/American): “the issues about which we spoke” versus informal “the issues we spoke about.” Both are understandable; the first is more formal.
Relative Pronoun Choice
- Which often follows for nonhuman antecedents in formal contexts. That can be used for restrictive clauses: “the method that we use.” British and American usage differ slightly in preference for which vs that, but both accept by which and in which when the writer chooses to front the preposition.
Recommendation
For high-formality writing (legal, academic), keep the preposition before which (no stranded preposition). For natural speech and less formal writing, stranded prepositions are fine.
Idiomatic Expressions
Common Idioms with In Which
- “A situation in which” is a frequent phrase: “a situation in which rules must be followed.”
- Parts of speech: a (article), situation (noun), in (preposition), which (relative pronoun), rules (noun), must (modal), be followed (passive verb phrase).
- Verb check: must be followed is modal + passive; it is correctly formed.
Common Idioms with By Which
- “The process by which” is often used in technical descriptions: “the process by which proteins fold.”
- Parts of speech: the (article), process (noun), by (preposition), which (relative pronoun), proteins (noun), fold (verb).
- Verb check: fold can be present tense when stating general truths; if narrating past lab results, use folded.
Combining Idioms Carefully
Some sentences combine time/location/means: “the chapter in which the process by which cells divide is described.” This is grammatical but heavy. Better to split for clarity: “the chapter in which cell division is described” or “the chapter that describes the process by which cells divide.”
Practical Tips
Tip 1: Ask the Question — Location or Means?
Before choosing, ask whether you need to mark location/time/containment or method/means/agent. If location or time, use in which; if means or instrument, use by which.
Tip 2: Keep Tenses Consistent
Match the tense in the relative clause to the main clause unless you intend to show a change in time. Example: “the method by which we collect data is reliable” (present-present) versus “the method by which we collected data was reliable” (past-past).
Tip 3: Avoid Awkward Heavy Constructions
If a phrase becomes long or dense, break it into two sentences. Heavy relative clauses make reading difficult. Example heavy: “the report in which the protocol by which samples were taken is recorded.” Revision: “the report records the protocol. It explains how samples were taken.”
Tip 4: Use Preposition Stranding When Natural
In spoken or informal writing, you can say “the room we met in” instead of “the room in which we met.” For formal writing, prefer in which.
Tip 5: Choose Which vs That Carefully
Use which with prepositions in formal contexts: “the policy by which benefits are distributed.” Use that for restrictive clauses without preposition fronting: “the policy that distributes benefits.”
Tip 6: Watch Passive Constructions
When by which occurs in passive sentences, it often links to an agent: “the tool by which the error was detected.” Check agent–verb agreement in passive forms: “was detected” matches singular error; “were detected” matches plural errors.
Tip 7: Be Careful With Sequence of Events
If an action in the relative clause happened before or after the main clause, use appropriate tense markers: “the year in which she had graduated” (past perfect) indicates graduation occurred before another past event.
Tip 8: Use Simple Tests
Replace the relative clause with a short phrase to test meaning:
- If “in which” can be replaced by “where” or “when”, it signals location/time.
- If “by which” can be replaced by “how” or “through which”, it signals means.
Example: “the way by which” → “the way how” is informal; better: “the way in which” (for manner) or “the way by which” (for means) depending on nuance.
Tip 9: Read Aloud to Check Flow
Reading sentences aloud highlights confusing preposition choice and tense mismatches. If the sentence sounds clumsy, revise.
Tip 10: Edit for Clarity and Brevity
Replace heavy relative clauses with active constructions when clarity improves: “The committee adopted a rule by which all members must vote” → “The committee adopted a rule requiring all members to vote.”
Conclusion
Choosing by which or in which depends on whether you want to mark means/agent/instrument (by which) or location/time/containment (in which). Keep parts of speech clear: articles before nouns, prepositions before relative pronouns, verbs in a tense that agrees with the subject and the time frame, and modifiers placed near the words they affect.
Avoid fragments by attaching relative clauses to a clear antecedent and avoid run-ons by splitting heavy clauses. Use preposition-fronting (in which, by which) in formal writing and preposition stranding in informal contexts when natural. Check passive constructions for correct agent marking and agreement, and prefer active voice or concise rephrasing when a sentence becomes overburdened. These steps will make your writing precise, readable, and appropriate for both American and British audiences.
FAQs
- When should I use “in which”?
The phrase in which marks location, containment, or time; use it when the relative clause describes where or when something happens. Example: “the room in which we met.” - When should I use “by which”?
Use by which to mark means, method, or agent; it often pairs with passive or technical descriptions. Example: “the method by which we measure growth.” - Can I end a sentence with “in” or “by” instead of saying “in which” or “by which”?
Yes. In informal writing or speech, preposition stranding is natural: “the room we met in.” For formal writing, prefer “in which” or rephrase to avoid ending with a preposition. - Is “the reason by which” correct?
“The reason by which” is awkward because reason calls for cause; use “the reason why” or “the reason for which” instead. - How do I check verb agreement in these clauses?
Identify the clause subject and match tense and number: “the meeting in which the team met“ (past, team singular or collective) or “the methods by which we collect data” (present, we plural). - Which is more formal, “in which” or “the place where”?
“In which” is more formal; “the place where” is natural and less formal. Choose based on register.
