Yes, “of which” is correct. It is a standard English construction that points back to something you just mentioned. “She read ten books, two of which were poetry” is a good sentence, and every major style guide accepts it.
The doubt is understandable. “Of which” sounds formal, it can feel heavy in casual writing, and its comma rules catch out even careful writers. This guide explains what it means, how to build sentences with it, where the comma goes, and how to rewrite it when it sounds stiff.
Quick answer: “Of which” joins a relative pronoun (“which”) to the preposition “of.” Use it for things, ideas, and groups that aren’t people. For people, use “of whom.”
Is It Correct to Say “Of Which”?
“Of which” is grammatically correct in standard British and American English. It is the preposition of attached to the relative pronoun which, and together they introduce a relative clause that adds information about a noun.
It does two main jobs.
The first is showing a part of a larger group: “The company has 40 offices, most of which are in Europe.” The second is showing that something belongs to, or is part of, the thing you just named: “He owns a house, the roof of which is made of slate.”
Both jobs come from the same idea. “Of” links a part to its whole, and “which” points back to the whole.
Why it sounds formal
You will meet “of which” most often in academic papers, legal writing, news reports, business documents, and books. In everyday speech, people usually pick something shorter, such as “and two of them were poetry” or “whose roof is slate.”
Formal does not mean wrong. It means the phrase suits some settings better than others. A grant proposal can carry “of which” easily. A text to a friend probably can’t.
“Of which” versus “of whom” versus “whose”
The choice depends on what the antecedent is, meaning the word or group the clause refers back to.
| Form | Refers to | Example |
|---|---|---|
| of which | things, animals, ideas, groups of objects | The museum owns 300 paintings, many of which are portraits. |
| of whom | people | She has four cousins, two of whom live abroad. |
| whose | people, and also things (possessive) | The house whose roof leaked was sold. |
“Whose” deserves a closer look. Older usage guides sometimes said it should only describe people, so “the house whose roof leaked” was thought to need “the house the roof of which leaked.” That view has faded. Current dictionaries and usage guides treat “whose” with inanimate nouns as acceptable, and often as the smoother choice.
So if “the roof of which” feels clumsy, “whose roof” is a legitimate swap.
Is it ever incorrect?
The phrase itself is fine, but sentences built around it can go wrong. Here are the usual problems:
- A doubled pronoun. “She bought six chairs, of which three of them were broken.” The words “of which” already stand for the chairs, so “of them” repeats the job.
- A missing antecedent. “Of which were broken” cannot start a sentence unless you have named the group first.
- The wrong pronoun for people. “He has five students, two of which are from Spain” should be “two of whom.”
- A comma splice. “She has six cars, three of them are electric” runs two full sentences together with only a comma. “Of which” fixes it: “She has six cars, three of which are electric.”
Correct any of these and the phrase works exactly as it should.
How to Use “Of Which” in a Sentence
The phrase almost always follows a noun, or a noun phrase, that names the group or thing you are describing. That noun is the antecedent. Then “of which” opens a clause that says something more about it.
The clause needs its own verb. That is the piece writers most often forget.
Pattern 1: quantifier + “of which”
This is the most common use. You state a whole, then say how much or how many of it fits a description.
Words that appear before “of which” in this pattern:
- one, two, three, and other numbers
- some, several, many, few
- most, all, none, both
- half, a majority, a handful, a number, the rest
Examples:
- The survey included 1,200 households, about half of which had children under ten.
- The town has four bridges, one of which dates to the 1800s.
- We tested nine prototypes, none of which passed the heat trial.
- The library holds thousands of manuscripts, the oldest of which is kept in a vault.
Pattern 2: noun + “of which”
Here the phrase links a part or feature to the whole. It works like a formal version of “whose.”
- The report cites several studies, the methods of which are questionable.
- She lives in a village, the name of which I can never remember.
- The building has a courtyard, the walls of which are covered in ivy.
The structure is: antecedent, the + noun + of which + verb. The same idea in plain English would be “whose methods are questionable.”
Pattern 3: preposition + noun + “of which”
Sometimes a longer phrase comes before “of which,” often with a place or position word.
- The city has a large park, at the center of which stands an old fountain.
- He wrote a novel, the final chapters of which were never published.
- The mountain has three peaks, on the tallest of which snow lies year-round.
These sentences sound polished, and they suit descriptive or academic writing. They can also read as dense, so check that a reader could follow them on a first pass.
Pattern 4: superlatives and ordinals
The words first, last, best, largest, oldest, and similar terms combine easily with “of which.”
- The company runs five plants, the largest of which employs 900 people.
- She has published four books, the first of which won a regional prize.
Pattern 5: restrictive use without a quantity
Less often, “of which” appears in a clause that is essential to the sentence, with no comma before it.
- This is the only novel of which I know the ending.
- It was a topic of which he had little knowledge.
This style is very formal. Most writers would say “the only novel I know the ending of” in ordinary prose.
Quick reference table
| Pattern | Structure | Example |
|---|---|---|
| Quantifier | whole, + quantifier + of which + verb | We hired ten interns, four of which stayed on. |
| Noun | whole, + the noun + of which + verb | The book, the cover of which is torn, sold quickly. |
| Preposition phrase | whole, + preposition + noun + of which | The lake, near the shore of which we camped, was frozen. |
| Superlative | whole, + the best/oldest/largest + of which | She owns six watches, the oldest of which is broken. |
| Restrictive | noun + of which + subject + verb | It is a question of which I am unsure. |
A simple method for building the sentence
Try this when you are unsure.
- Write the main sentence first: “The firm has twelve clients.”
- Write the extra fact as its own sentence: “Seven are based overseas.”
- Replace the noun or pronoun that repeats the group with “of which,” and move the phrase to the front of the clause: “of which seven are based overseas.”
- Bring the pieces together with a comma: “The firm has twelve clients, seven of which are based overseas.”
Once you have done this a few times, the shape becomes automatic.
Getting the verb right
The verb in the “of which” clause agrees with the word before “of which,” not with the antecedent.
- “One of which was damaged.” (one is singular)
- “Two of which were damaged.” (two is plural)
- “Much of which is unreadable.” (much takes a singular verb)
- “All of which are available online.” (all here refers to plural items)
With words like “all,” “most,” “some,” and “half,” the verb depends on what is being counted. If the noun is uncountable, use a singular verb: “Most of which is water.” If it is a plural group, use a plural verb: “Most of which are small.”
A few sentences to test yourself
Which of these are correct?
- A. The team submitted eight proposals, three of which were funded.
- B. The team submitted eight proposals, three of them were funded.
- C. The team submitted eight proposals, three of which they were funded.
Only A works. B is a comma splice, and C has a stray pronoun (“they”) that doesn’t belong.
Comma With “Of Which”
Comma placement is where most questions about this phrase start. The good news is that a small set of rules covers nearly every case.
The core rule
A comma goes before the whole “of which” phrase when the clause adds extra information. The comma does not go between the quantifier and “of which.”
- Correct: She has six cars, three of which are electric.
- Incorrect: She has six cars three, of which are electric.
- Incorrect: She has six cars, three, of which are electric.
The words “three of which” travel as a unit. The comma sits in front of the unit.
Nonrestrictive versus restrictive clauses
Grammar guides describe two kinds of relative clause.
A nonrestrictive clause adds extra detail. You could delete it and the main sentence would still make sense. It takes a comma.
A restrictive clause is needed to identify which thing you mean. Delete it and the meaning changes. It takes no comma.
| Clause type | Comma? | Example |
|---|---|---|
| Nonrestrictive (extra information) | Yes | The council approved 20 permits, most of which were for housing. |
| Restrictive (essential information) | No | It is a subject of which few people are aware. |
Most “of which” sentences with a quantifier are nonrestrictive, so they take a comma. Sentences with the phrase after a noun and no quantity are more mixed, so apply the deletion test.
The deletion test
Take out the clause and read what is left.
- “The house, the roof of which is slate, was sold.” Without the clause: “The house was sold.” That still works, so the commas stay.
- “It is the only report of which I have a copy.” Without the clause: “It is the only report.” That changes the meaning, so no comma.
If the sentence still makes sense and says the same thing, use the comma. If the meaning shifts, leave it out.
Commas around a mid-sentence clause
When the “of which” clause lands in the middle of a sentence, put a comma on both sides.
- The house, the roof of which is made of slate, has stood since 1902.
- The bridges, two of which are closed for repairs, connect the north and south banks.
Skipping the second comma is a common slip. It leaves the clause hanging, and the sentence loses its rhythm.
The comma splice trap
A comma splice happens when two complete sentences are joined by only a comma. “Of which” is one of the cleanest cures, because it turns the second sentence into a dependent clause.
| Comma splice | Fixed with “of which” |
|---|---|
| We visited five cities, two were in Spain. | We visited five cities, two of which were in Spain. |
| The exam had 50 questions, most were multiple choice. | The exam had 50 questions, most of which were multiple choice. |
| She wrote ten reports, the last was rejected. | She wrote ten reports, the last of which was rejected. |
That trick is worth remembering if you often catch yourself writing “…, two of them were…”.
What about “which of”?
Do not confuse “of which” with “which of.” The second appears in questions and in a different type of clause.
- “Of which” (relative): The team tested six designs, two of which failed.
- “Which of” (question): Which of the six designs failed?
Commas follow different rules in the second case, and you seldom need one in a direct question.
Alternatives to Using “Of Which”
You can always rewrite a sentence without “of which.” That is often smart when the phrase makes a sentence too long or too formal for your reader.
Here is a comparison of the main options:
| Option | Example | Tone |
|---|---|---|
| of which | The firm has twelve clients, seven of which are overseas. | Formal |
| whose | The book whose cover is torn sold quickly. | Neutral to formal |
| of them (with a new clause) | The firm has twelve clients, and seven of them are overseas. | Everyday |
| which… of | The topic which I know little of is law. | Casual, slightly loose |
| new sentence | The firm has twelve clients. Seven are overseas. | Plain, clear |
Two of these, “which… of” and “new sentence,” need a closer look.
Which… Of
In this approach, the pronoun moves to the front of the clause and the preposition drops to the end. Grammarians call this preposition stranding.
- Formal: This is the book of which I am most proud.
- Relaxed: This is the book which I am most proud of.
- Even simpler: This is the book I am most proud of.
The old rule that a sentence must never end with a preposition is a myth. It came from an attempt to force English into Latin patterns, and modern style guides reject it. Ending a clause with “of” is normal in speech and in most writing.
That said, the swap does not work everywhere. It succeeds when “of” belongs to a verb or adjective phrase:
| Formal | Rewritten |
|---|---|
| It is a topic of which he knows little. | It is a topic which he knows little of. |
| The award of which she was so proud. | The award which she was so proud of. |
| A film of which everyone spoke. | A film which everyone spoke of. |
It fails when “of which” follows a quantifier or a part-and-whole noun:
- “She has six cars, which three of are electric.” This is not English.
- “The house which the roof of is slate.” This is not English either.
So use “which… of” only where the preposition is tied to a verb or adjective. For the “three of which” pattern, look at the next option.
Notice too that “that” and the bare form sound more natural than “which” in the relaxed versions. “The book that I’m proud of” and “the book I’m proud of” are both easy to read.
New Sentence
This is the simplest and often the best fix. Split the long sentence into two, and let the second one carry the detail.
| With “of which” | As two sentences |
|---|---|
| The report contains 40 pages, most of which are charts. | The report contains 40 pages. Most are charts. |
| The company opened six stores, two of which closed within a year. | The company opened six stores. Two closed within a year. |
| We interviewed 30 candidates, the best of which had a decade of experience. | We interviewed 30 candidates. The best had a decade of experience. |
| The city has many parks, several of which host free concerts. | The city has many parks. Several host free concerts. |
Shorter sentences suit web writing, instructions, and anything read on a phone. They lower the chance that a reader loses the thread.
They also give you more control over emphasis. In “Two closed within a year,” the fact stands alone. Inside a longer sentence with “of which,” it is one part among several.
You don’t need to strip out every “of which.” A few, used with care, add variety and a measured tone. A page full of them can feel stiff. Choose based on your reader.
How to choose
Some questions can settle it fast.
- Who is reading? A colleague on Slack wants short. A journal editor may prefer the formal form.
- How long is the sentence? If it has already passed 30 words, split it.
- Does the phrase read aloud smoothly? If you stumble, rewrite it.
- Does your style guide have a view? Follow it. Chicago, AP, and most house guides accept “of which” and “whose” alike.
What to Remember
Here are the main points in one place.
- “Of which” is correct English. It suits things and groups that are not people.
- Use “of whom” for people, and “whose” as a smooth option for either.
- The phrase needs an antecedent before it and a verb after it.
- Put the comma before the whole phrase in nonrestrictive clauses: “six cars, three of which are electric.”
- Skip the comma when the clause is essential to the meaning.
- The verb agrees with the quantifier (“one of which was,” “two of which were“).
- Avoid doubling up with “of them,” “they,” or “it” inside the clause.
- When the phrase feels heavy, try “whose,” “which… of,” or a fresh sentence.
Frequently Asked Questions
Is “of which” formal or informal?
It is formal to neutral. It reads well in essays, reports, and news, while speech usually favors “of them.”
Can I start a sentence with “of which”?
Only in a few fixed cases, such as “Of which more later.” Normally, name the group first and follow with “of which.”
Do I need a comma before “of which”?
Usually yes, when the clause adds extra information, as in “ten books, two of which were poetry.” Leave it out when the clause is essential.
Is “of which” the same as “whose”?
They often overlap: “the roof of which” and “whose roof” carry the same meaning. “Whose” is shorter and usually smoother.
Can I use “of which” for people?
No. Use “of whom” for people: “three sons, two of whom are teachers.”
Is it wrong to end a sentence with “of”?
No. “This is the book I’m proud of” is standard English, and the old rule against it is a myth.
How do I fix “three of them” after a comma?
Replace “them” with “which” and remove the extra pronoun: “six cars, three of which are electric.” Or split it into two sentences.
Conclusion
“Of which” is a useful, fully correct part of English. It links a part to its whole, adds detail without a second sentence, and cures many comma splices in one stroke.
The rules are short. Name the group first, give the clause its own verb, place the comma before the phrase when the information is extra, and match the verb to the quantifier. When the phrase feels too heavy, “whose,” “which… of,” or two shorter sentences are always available.