1. One relationship, two preposition positions
A preposition shows how a thing relates to an action: we rely on a resource, refer to a document or work under conditions. Which represents that thing in a relative clause. The preposition can directly precede which: the resource on which we rely.
This fronting is characteristic of formal reports, academic writing and official explanations. A preposition at the clause’s end is also grammatical and often more natural in conversation. Style does not make the less formal pattern an error.
noun + preposition + which + subject + predicate
- subject / S —
- The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
- noun —
- A word naming a person, thing or idea: student, book, happiness.
- preposition —
- A word showing a relationship, such as in, on or from: from Ukraine.
The evidence on which the conclusion rests is incomplete.
The evidence on which the conclusion rests is incomplete.
Rest on retains on; which refers to evidence.
The evidence which the conclusion rests on is incomplete.
The evidence which the conclusion rests on is incomplete.
The same meaning; final on is a grammatical, less formal alternative.
2. Choose the preposition for the relationship, not its sound
First reconstruct the simple statement: we refer to the appendix → the appendix to which we refer. Formality changes the preposition’s position, not the verb’s complement pattern. Depend on or depend upon gives on which or upon which; refer to gives to which.
Abstract nouns also have established patterns: to a certain extent → the extent to which; under these conditions → the conditions under which. Prepositions are not arbitrary decorations. In spatial contexts, in, at and under can create different true descriptions: choose the one that accurately identifies the position.
The appendix to which the author refers contains the figures.
The appendix to which the author refers contains the figures.
We refer to something, so to remains before which.
We assessed the extent to which noise affected concentration.
We assessed the extent to which noise affected concentration.
Extent describes degree of effect rather than manner; the target pattern is to which.
The conditions under which the samples were stored were stable.
The conditions under which the samples were stored were stable.
The underlying relationship is stored under these conditions; conditions are not a location inside a container.
3. Which cannot disappear after a fronted preposition
When a relative clause refers to a thing, a fronted preposition takes which rather than relative that. Do not leave only the preposition without a relative pronoun. Subject and predicate normally follow which; the order does not become interrogative.
This restriction concerns relative that. Ordinary After that, we left is correct: that means the preceding situation and does not introduce a relative clause. For a person, the typical formal pattern is preposition + whom; which is not universal after all prepositions.
The proposal for which we voted was adopted.
The proposal for which we voted was adopted.
For which replaces for the proposal; the pronoun is necessary.
The adviser with whom we consulted recommended a review.
The adviser with whom we consulted recommended a review.
Adviser is a person. This is a brief contrast; the main practice concerns things.
After that, the team revised the timetable.
After that, the team revised the timetable.
That is demonstrative rather than relative, so no rule is broken.
4. Commas depend on information, not the preposition
Preposition + which can occur in a defining relative clause identifying a thing or a clause adding extra information. If the description answers “which one among several?”, use no commas.
If the thing is already uniquely identified, set off the extra information with commas. Inside a sentence, two commas are needed. Do not automatically add them merely because which appears or the style is formal: that can change how the reader identifies the thing.
The file to which the letter refers is missing.
The file to which the letter refers is missing.
The reference identifies the relevant file among others; no commas.
File A, to which the letter refers, is missing.
File A, to which the letter refers, is missing.
File A already identifies the file; the letter’s reference is extra information between commas.
5. Restructuring without repetition or new facts
When formalising, move the existing preposition before which and remove its old copy. Do not repeat it or them after the verb for the same thing, already represented by which. Other objects needed by the meaning can remain.
Preserve negation, time frame, participants and strength of claim. Changing which to that and adding strictly are different edits: strictly adds intensity rather than repairing a relative construction. When joining sentences, retain both sets of facts without accidentally strengthening either.
The system which we depend on is expensive.
The system which we depend on is expensive.
A grammatical original version for a change of style.
The system on which we depend is expensive.
The system on which we depend is expensive.
On has moved once; there is no extra on or it after depend.
The conditions under which the trial took place were controlled.
The conditions under which the trial took place were controlled.
Controlled does not automatically mean strictly controlled; do not add unsupported intensity.
6. Limits: where, direct objects and verb particles
Not every which needs a preposition. In the report which I read, read takes a direct object, so invent no preposition. Nor can every where mechanically become in which: distinguish departure from a place, movement to it and presence in it.
Do not move a phrasal-verb particle as though it were a preposition. In give up a habit, up belongs to the verb meaning “abandon”: the habit which I gave up. Up which I gave does not express this pattern. Complex phrasal-prepositional verbs are not developed into a separate topic here.
The report which I read yesterday was clear.
The report which I read yesterday was clear.
Read the report has a direct object; this is a boundary of the pattern, not a reason to add to.
The office from which the parcels were sent has closed.
The office from which the parcels were sent has closed.
From expresses the source of dispatch, rather than presence inside.
The habit which she gave up was checking emails at midnight.
The habit which she gave up was checking emails at midnight.
Up is the particle of give up and stays with the verb.
7. A practical check for your own sentence
Name the thing which refers to. Reconstruct a simple statement and check the preposition: depend on the grant, refer to the table, work under the conditions. If that relationship does not work, correct the meaning before the word order.
Then check the text’s purpose: is formal fronting needed, and does the description identify the thing or merely add information? Your own message can use different natural words and structures while preserving meaning and the preposition’s relationship to the verb or noun.
We need to review the assumptions on which this forecast is based.
We need to review the assumptions on which this forecast is based.
Forecast is based on assumptions: a clear relationship and suitable formal relative description.
The pilot scheme, under which residents received free advice, has ended.
The pilot scheme, under which residents received free advice, has ended.
An already identified scheme receives an extra description; commas enclose the entire relative clause.
Common mistakes
Incorrect:The clause to that the note refers is unclear.
Correct:The clause to which the note refers is unclear.
A fronted to requires relative which rather than that; refer to is preserved.
Incorrect:The fund on which we rely on is temporary.
Correct:The fund on which we rely is temporary.
On already precedes which. The second copy has no separate object and repeats the relationship.
Incorrect:The archive in we found the letters is open.
Correct:The archive in which we found the letters is open.
A relative pronoun cannot be omitted after fronted in.
Incorrect:The model on which we depend on it is outdated.
Correct:The model on which we depend is outdated.
Which already represents model. Do not repeat on it after depend.