Basics. Fronted Prepositions in Relative Clauses: correct answers
Jump to answers ↓What "Fronting" a Preposition Means
In everyday English, when a relative clause contains a preposition, most people stick the preposition at the end:
That's the hotel that we stayed at.
There's another option: move the preposition to the front of the relative clause, right before the relative pronoun. When you do this, you must use whom (for people) or which (for things) — never that, and never leave the pronoun out:
That's the hotel at which we stayed.
This is called a fronted preposition (sometimes "pied-piping," if you like linguistic jargon). The meaning doesn't change, but the sentence sounds more formal and more precise. You'll meet it constantly in academic writing, official reports, and literary prose.
How the Pattern Works — Two Worked Examples
Example 1 — thing (which)
Imagine you want to combine these two ideas: The bridge was built in 1890. We walked across the bridge.
✅ The bridge across which we walked was built in 1890. ❌ The bridge across that we walked was built in 1890.
The second sentence is wrong because that cannot follow a preposition. Once you pull the preposition to the front, you need which.
Example 2 — person (whom)
Combine: The colleague helped me a lot. I was working with the colleague.
✅ The colleague with whom I was working helped me a lot. ❌ The colleague with who I was working helped me a lot.
After a fronted preposition, the correct form for people is whom, not who. In casual speech people bend this rule, but in writing — and certainly in exams — whom is expected.
When to Front and When Not To
Fronting the preposition is optional in most sentences. You can always leave it at the end instead:
The colleague who/that I was working with helped me a lot.
Both versions are grammatically correct. The fronted version is simply more formal.
However, there are contexts where fronting sounds strange and you should avoid it:
- Phrasal verbs. If the preposition is really a particle that belongs tightly to the verb, don't front it. Nobody writes "The noise up with which I will not put" — that's a famous joke, not real English. Keep phrasal-verb particles at the end: the noise that I won't put up with.
- Informal registers. In a text message or chatty email, "the guy to whom I was talking" can sound oddly stiff. Match your register.
On the other hand, fronting is almost expected when the sentence already has a formal tone — contracts, research papers, or any writing where clarity and precision matter more than warmth.
The Mistake B1–B2 Learners Make Most Often
The single most common error is using that after a fronted preposition:
❌ The project in that she was involved required extra funding. ✅ The project in which she was involved required extra funding.
This happens because learners know that works as a general-purpose relative pronoun, and it does — but only when the preposition stays at the end (the project that she was involved in). The moment you move the preposition forward, that is no longer allowed. Swap it for which (things) or whom (people), and the problem disappears.
A related slip is doubling the preposition — fronting it and accidentally leaving a copy at the end:
❌ The city in which we grew up in was tiny. ✅ The city in which we grew up was tiny.
If you've moved the preposition to the front, it's already doing its job. Delete the leftover one at the end.
Keep these two checks in mind — no that after a preposition, and no doubled preposition — and fronted relative clauses become a reliable tool for making your writing sound polished and precise.
Correct answers
Question 1
The correct answers are The monarch to whom the secret letter was addressed never received it. and The controversial treaty upon which the two nations agreed was signed in 1812.
In highly formal English, prepositions are often placed before the relative pronoun rather than at the end of the clause.
When placing a preposition before a relative pronoun, you must use whom (for people) or which (for things). You cannot use who or that immediately after a preposition.
While "The monarch whom the secret letter was addressed to..." is grammatically valid in everyday English, it leaves the preposition stranded at the end, which does not fit the strict formal requirement of "fronting" the preposition asked for in the prompt.
Question 2
Help the detective complete her dramatic final report by choosing the grammatically correct option.
The mysterious informant _____ the detective confided turned out to be the mastermind all along!
The correct answer is in whom.
In formal English, prepositions (like "in") are placed before the relative pronoun. When referring to a person immediately following a preposition, you must use the objective case whom. You cannot use "who" or "that" right after a preposition in a relative clause!
Question 3
Complete the spaceship captain's bizarre daily log by choosing the correct formal prepositional phrase for each gap.
The highly advanced alien species with which we just made contact unexpectedly offered us a platter of space-tacos. Meanwhile, the mysterious glowing orb for which we are now responsible has started humming an upbeat pop tune. I am beginning to suspect that the uncharted galaxy from which our ship just emerged is actually a giant cosmic amusement park.
The highly advanced alien species with which we just made contact unexpectedly offered us a platter of space-tacos.
The phrase is "make contact with someone/something." In a formal relative clause, the preposition "with" shifts to the front of "which."
Meanwhile, the mysterious glowing orb for which we are now responsible has started humming an upbeat pop tune.
The adjective "responsible" is followed by the preposition "for" (responsible for the orb).
I am beginning to suspect that the uncharted galaxy from which our ship just emerged is actually a giant cosmic amusement park.
The verb "emerge" pairs with the preposition "from" (emerge from the galaxy).
Question 4
The correct answers are The crystal glasses in which the vintage wine is served must be polished twice. and The dignitaries to whom you will serve afternoon tea are seated in the parlor.
Just like Mr. Belvedere's uniform, formal grammar has strict rules! When a preposition is moved to the front of a relative clause, it can only be followed by which (for objects like glasses) or whom (for people like dignitaries).
"In that" and "to who" are grammatically incorrect.
The sentence ending in "...resides in" is grammatically acceptable in standard English, but it strands the preposition at the end, failing Mr. Belvedere's strict formal requirement.
Question 5
Complete the snooty food critic's latest scathing review by selecting the correct formal phrase.
The alarming enthusiasm _____ the waiter presented the deep-fried grasshoppers completely ruined my appetite.
The correct answer is with which.
We do things "with enthusiasm," so the relative clause needs the preposition "with." In a formal register, the preposition is moved to the front of the relative clause, right before which. Remember, the relative pronoun "that" can never immediately follow a preposition!
Question 6
The correct answers are from which and with whom.
In official or formal registers, we avoid ending a sentence with a preposition (preposition stranding) by moving the preposition before the relative pronoun.
- A transmission originates from a place, giving us "from which." ("That" cannot follow a preposition).
- You negotiate with someone. When referring to a person after a preposition, you must use the objective case "whom," giving us "with whom."
Question 7
Help the detective complete her formal report on the great penguin heist by choosing the correct prepositional phrase for each clause.
The exact extent to which the zookeeper was involved remains a heavily guarded secret. Furthermore, the absurd premise on which the entire heist was based makes absolutely no logical sense. Finally, the highly suspicious manner in which the penguin vanished suggests a mastermind at work.
The exact extent to which the zookeeper was involved remains a heavily guarded secret.
We use "to which" because the standard phrase is "the extent to something."
Furthermore, the absurd premise on which the entire heist was based makes absolutely no logical sense.
We use "on which" because we "base something on a premise."
Finally, the highly suspicious manner in which the penguin vanished suggests a mastermind at work.
We use "in which" because things happen "in a certain manner."
Question 8
The correct answers are We discovered fifty critical bugs, most of which were caused by the recent update. and I spoke directly to the senior engineers, several of whom denied any responsibility.
When combining quantifiers (like most, several, all, none) with a preposition (usually of) in a relative clause, you must use which for things and whom for people.
"Most of that" and "several of who" are incorrect.
Additionally, "most of which they were caused" is incorrect because "which" already acts as the subject of the relative clause; adding "they" creates a double subject!
Question 9
The correct answers are to whom and under which.
In highly formal English, prepositions are placed before the relative pronoun rather than at the end of the clause.
- We say "addressed a letter to someone," so the formal relative structure is "to whom." ("Who" cannot be used immediately after a preposition).
- We say "operate under conditions," so the formal relative structure is "under which." ("That" can never be used immediately after a preposition in a relative clause).
Question 10
Help the eccentric professor complete his rather alarming report to the safety committee.
The highly explosive chemical compound _____ yesterday has mysteriously vanished from the laboratory.
The correct answer is with which I was experimenting.
The verb phrase is "experiment with." In formal writing, we shift the preposition to the beginning of the relative clause ("with which").
Watch out for the sneaky double preposition trap! If you move "with" to the front, you cannot leave another "with" at the end of the clause.
Question 11
The correct answers are upon which and to which.
When a preposition is moved to the front of a relative clause, it must match the verb or noun it belongs to.
- A foundation is built upon (or on), so we use "upon which." We cannot use "that" directly after a preposition.
- The noun "extent" strongly collocates with the preposition "to" (e.g., "to a great extent"). Therefore, the correct formal relative phrase is "the extent to which."
Question 12
Complete the stressed college student's complaint about their thesis by choosing the correct formal relative clause for each blank.
The esteemed professor on whose approval my entire academic future depends just sighed heavily at my first draft. Worse still, the obscure historical texts to which I am referring throughout the essay were mostly found on a dubious fan forum. To top it all off, the study group members with whom I collaborated spent the whole time watching cat videos!
The esteemed professor on whose approval my entire academic future depends just sighed heavily at my first draft.
We say "depend on someone's approval." Because the approval belongs to the professor, we use the possessive relative pronoun "whose" combined with the preposition "on."
Worse still, the obscure historical texts to which I am referring throughout the essay were mostly found on a dubious fan forum.
The verb "refer" takes the preposition "to" (refer to texts). In formal English, the preposition moves before the relative pronoun "which."
To top it all off, the study group members with whom I collaborated spent the whole time watching cat videos!
You "collaborate with someone." Since the members are people, we use the object pronoun "whom" after the preposition "with."