Simple explanation
What makes relative clauses advanced at C1 level? At lower levels, relative clauses are often used simply to identify or describe a person or thing, as in The woman who lives next door is a doctor. At C1 level, relative structures become more flexible. They can express relationships involving quantity, possession, circumstances, time, consequence, degree, and links between entire propositions. Register also becomes important: choosing between structures such as the person I spoke to and the person to whom I spoke affects formality and style. Defining and non-defining relative clauses A defining relative clause contains information that is necessary to identify the noun. It is normally written without commas. A non-defining relative clause adds extra information about a person or thing that is already identifiable and is separated by commas. That cannot normally replace who or which in a non-defining clause. At C1 level, punctuation matters because the presence or absence of commas can significantly change meaning. What is preposition stranding? In neutral and conversational English, a preposition often remains at the end of the relative clause. This is called preposition stranding: The person who I spoke to was very helpful. If the relative pronoun is an object in a defining clause, it may also be omitted: The person I spoke to was very helpful. This structure is standard and very common in modern spoken English. What is preposition fronting? In more formal English, the preposition can be moved in front of the relative pronoun: The person to whom I spoke was very helpful. This is called preposition fronting. After a fronted preposition, whom is normally used for people and which for things or abstract concepts. That cannot be used in this position, and the relative pronoun cannot be omitted. Quantifier + of + relative pronoun Advanced relative clauses can combine quantifiers such as many, several, some, most, all, neither, or none with of whom or of which. For example: The researchers, several of whom had worked abroad, joined the project. Whom refers to people, while which refers to things, ideas, or situations. These structures are especially useful in formal, academic, and professional writing. Using which to refer to an entire clause Which does not always refer to a single noun. In a non-defining clause, it can refer to the entire statement before it: He missed the deadline, which surprised everyone. Here, which refers to the fact that he missed the deadline. This pattern is useful for adding a consequence, reaction, evaluation, or comment about a complete situation. Advanced structures with which At C1 level, combinations such as in which case, at which point, by which time, and for which reason allow speakers and writers to connect ideas with greater precision. For example, You may need further evidence, in which case we can extend the review period. These structures compress information that might otherwise require a separate sentence or a longer conditional expression.
Grammar formula
Defining relative clause
noun + who/which/that + clauseThe researcher who developed the model received an award.
Non-defining relative clause
noun + , who/which/whom + clause ,The researcher, who had worked abroad for years, returned to the university.
Preposition stranding
noun + who/which/that/Ø + subject + verb + prepositionThe colleague who I was talking to has left.
Preposition fronting with a person
person + preposition + whom + subject + verbThe colleague to whom I was talking has left.
Preposition fronting with a thing
thing + preposition + which + subject + verbThe framework within which the policy operates is complex.
Quantifier relative structure
noun + , quantifier + of whom/which + clause ,The candidates, three of whom had previous experience, were interviewed.
Whole-clause which
main clause + , which + clauseThe server failed again, which caused a major delay.
Advanced connector with which
main clause + , in/at/by/for which + noun + clauseThe system may reject the request, in which case you should contact support.
Core rules
- 1
Object relative pronouns can sometimes be omitted
If who, which, or that functions as the object in a defining relative clause, it can often be omitted: The report (that) I submitted was accepted. If the pronoun is the subject, it cannot be omitted: The report that explains the issue is attached.
- 2
Do not use that in non-defining relative clauses
After a comma, use who or whom for people and which for things or ideas. For example: My supervisor, who works in Montreal, reviewed the paper. The form My supervisor, that works in Montreal, is not standard.
- 3
Use whom or which after a fronted preposition
Use whom for people: the colleague with whom I worked. Use which for things or abstract concepts: the method on which the analysis was based.
- 4
Do not omit the relative pronoun after a fronted preposition
The company for I worked is incorrect. The correct formal structure is The company for which I worked. In a less formal style, The company I worked for is natural and correct.
- 5
Do not use that after a fronted preposition
Structures such as to that, with that, or about that are not used as formal relative structures. Use whom for people and which for things: the person to whom I spoke or the issue about which we spoke.
- 6
Use whom for people and which for things after quantifiers
Use structures such as several of whom, many of whom, and none of whom for people. Use several of which, many of which, and none of which for things, ideas, or situations.
- 7
Which can refer to the whole previous clause
After a comma, which can summarize the entire event or proposition before it: She rejected the proposal, which created further delays. Which refers to her rejecting the proposal, not simply to the noun proposal.
- 8
Choose the preposition from the original expression
The preposition is determined by the verb, adjective, or noun in the original phrase. For example: depend on becomes on which, speak to becomes to whom, be responsible for becomes for which, and be associated with becomes with which.
Useful examples
The committee interviewed twelve candidates, three of whom had previously worked overseas.
The committee interviewed twelve people, and three of those candidates had worked abroad before.
Three of whom refers to three people within a previously mentioned group.
The theory on which the entire argument is based has recently been challenged.
The whole argument depends on a theory that has recently been questioned.
On which is the formal fronted form of based on.
The person to whom you should address your complaint is currently unavailable.
The person who should receive your complaint is not available at the moment.
To whom is more formal than who you should address your complaint to.
The apartment we moved into last year has already been sold.
The apartment that became our home last year has already been sold.
The object relative pronoun is omitted, while into remains at the end of the clause.
The apartment into which we moved last year has already been sold.
The apartment we entered as our new home last year has already been sold.
Into which is the more formal equivalent of the previous example.
Several measures were introduced, none of which proved effective in the long term.
A number of measures were introduced, but not one of them worked effectively over time.
None of which refers to none of the previously mentioned measures.
She declined the offer, which came as a surprise to the entire team.
She refused the offer, and her decision surprised everyone on the team.
Which refers to the whole action of declining the offer.
The conditions under which the experiment was conducted were carefully controlled.
The experiment was carried out in conditions that were carefully controlled.
Under which is especially common in academic and formal writing.
The conference ends on Friday, by which time we expect to have reached an agreement.
The conference finishes on Friday, and we expect an agreement to be completed before then.
By which time means no later than the previously mentioned time.
You may be asked to provide additional documentation, in which case the process will take longer.
You may need to provide more documents, and if that happens, the process will take more time.
In which case introduces a consequence that depends on the previous situation.
The negotiations continued until midnight, at which point both sides agreed to postpone the decision.
The talks continued until midnight, and then both sides agreed to delay the decision.
At which point refers to a specific moment or stage in an unfolding process.
My former supervisor, with whom I still collaborate occasionally, has published a new study.
My former supervisor, who still works with me from time to time, has published a new study.
With whom is used in a formal non-defining relative clause.
The software contains several security features, two of which operate automatically.
The software has several security functions, and two of them work automatically.
Two of which identifies two items from a group of things.
The extent to which social factors influence the outcome remains unclear.
It is still unclear how strongly social factors affect the final result.
The extent to which is a highly useful formal structure meaning how much or to what degree.
That is the principle according to which all applications are evaluated.
That is the rule that is used as the basis for evaluating every application.
According to which shows that multi-word prepositional expressions can also be fronted.
Common mistakes
- ❌ The manager to who I spoke was helpful. ✅ The manager to whom I spoke was helpful. After the fronted preposition to, formal English requires the object form whom when referring to a person.
- ❌ The project on that we are working is confidential. ✅ The project on which we are working is confidential. That cannot directly follow a fronted preposition. Use which for things or abstract concepts.
- ❌ The company for I worked closed last year. ✅ The company for which I worked closed last year. A relative pronoun cannot be omitted after a fronted preposition.
- ❌ My brother, that lives in Canada, is visiting next month. ✅ My brother, who lives in Canada, is visiting next month. That is not normally used in non-defining relative clauses.
- ❌ The students, many of which had never travelled abroad, were nervous. ✅ The students, many of whom had never travelled abroad, were nervous. Students are people, so whom is required after many of.
- ❌ The system crashed, that caused us to lose several hours of work. ✅ The system crashed, which caused us to lose several hours of work. Which, not that, can refer back to the entire previous clause.
- ❌ The framework within that the organisation operates is highly regulated. ✅ The framework within which the organisation operates is highly regulated. A fronted preposition such as within must be followed by which when the antecedent is not a person.
- ❌ The researcher, whom developed the method, received an award. ✅ The researcher, who developed the method, received an award. The relative pronoun is the subject of developed, so who is required. Whom is an object form.
Learning tips
- When a preposition is fronted, first check whether the antecedent is a person or a thing: person → whom, thing → which.
- Recover the original verb-preposition combination before moving the preposition: rely on, speak to, work with, be based on.
- Preposition fronting is not inherently better English. It is mainly a more formal stylistic choice.
- Pay close attention to commas in non-defining clauses because punctuation can change meaning.
- In structures such as many of whom or several of which, the reference group should be clearly identified immediately before the relative clause.
- Useful academic patterns include the extent to which, the context in which, the basis on which, and the conditions under which.
- Do not make a sentence complex simply to sound advanced. At C1 level, accuracy, register, and clarity matter more than grammatical decoration.
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PlannedRelated grammar
Related dictionary words
Frequently asked questions
Is it grammatically wrong to end a relative clause with a preposition?
No. Sentences such as The person I spoke to are standard and extremely common in modern English. The person to whom I spoke is simply more formal.
When should I use whom instead of who?
Whom is used when the relative pronoun functions as an object, especially after a fronted preposition: the person to whom I wrote. In everyday English, who is often used in object position, or the pronoun may be omitted entirely.
Why is to whom correct but to who usually avoided in formal English?
After the preposition to, the relative pronoun functions as an object. Formal English therefore uses the object form whom.
Can I use that after a preposition?
Not in preposition fronting. Use forms such as with whom, about which, or through which. That can appear in a defining clause when the preposition remains later in the sentence, as in the issue that we talked about.
What is the difference between The students who passed and The students, who passed?
Without commas, the clause identifies which students are meant: the ones who passed. With commas, the group is already identified, and the fact that they passed is presented as additional information.
When does which refer to an entire sentence?
It can refer to the whole previous clause when it introduces a reaction, result, or evaluation. For example, He cancelled the meeting, which annoyed everyone means that the cancellation itself annoyed everyone.
Are many of whom and several of which only used in academic English?
No. They also occur in general standard English, but they are particularly common in formal, academic, professional, and journalistic writing because they combine information efficiently.
Is preposition fronting always better at C1 level?
No. C1 proficiency means choosing a structure that fits the context. Fronting may suit formal writing, while stranded structures such as who I worked with or which I relied on are often more natural in conversation.