A contact clause (also called a zero relative clause) is a defining relative clause in which the relative pronoun — that, which, who or whom — has been left out. The main clause and the relative clause are placed directly next to each other, "in contact," with nothing joining them: The book I read was excellent. (compare: The book that I read was excellent.)
Contact clauses are one of the most common features of natural spoken and informal written English. Knowing the rule for when you can and cannot omit the pronoun will make your English sound far more fluent — and help you avoid a handful of very common mistakes.
The Core Rule: Object vs. Subject
The relative pronoun can be omitted only when it is the object of the verb inside the relative clause. If the relative pronoun is the subject of the relative clause, it can never be dropped.
- Object (can omit): The book (that) I read was excellent. — "I" is the subject of "read"; "that" is the object, so it can be dropped.
- Object (can omit): The man (who) I met yesterday works here. — "I" is the subject of "met"; "who" is the object.
- Subject (cannot omit): The man who called is my uncle. — "who" is the subject of "called," so it must stay.
- Wrong: The man called is my uncle. — without "who," this no longer means the same thing; it reads like a reduced passive clause ("the man who was called").
A quick test: look at the verb immediately after the gap where the pronoun would go. If there is already a subject (a noun or pronoun like "I," "she," "we") between the gap and the verb, the relative pronoun was the object and can be dropped. If the verb comes immediately after the gap with no subject in between, the relative pronoun was the subject and must stay.
More Examples: With and Without the Pronoun
- This is the film (that) everyone is talking about. (object of "about")
- Have you seen the keys (that) I left on the table? (object of "left")
- She's the teacher (who) we all admired at school. (object of "admired")
- The restaurant (which) they recommended was fully booked. (object of "recommended")
- Is this the email (that) you were waiting for? (object of "for")
- The people who live next door are very friendly. (subject of "live" — cannot omit)
- The car that broke down last week is finally fixed. (subject of "broke down" — cannot omit)
- The dress (that) I bought yesterday doesn't fit. (object of "bought")
Comparing Omissible and Obligatory Relative Pronouns
| Sentence | Role of pronoun | Can omit? |
|---|---|---|
| The song (that) I heard on the radio was catchy. | Object of "heard" | Yes |
| The song that was playing on the radio was catchy. | Subject of "was playing" | No |
| The colleague (who) I emailed hasn't replied. | Object of "emailed" | Yes |
| The colleague who emailed me hasn't replied. | Subject of "emailed" | No |
| My father, who is a teacher, called this morning. | Subject, non-defining clause (commas) | No |
| The house (that) we visited last summer is for sale. | Object of "visited" | Yes |
| The man to whom I spoke was very helpful. | Object of preposition "to" (formal, fronted) | No |
| The man (who/that) I spoke to was very helpful. | Object of preposition "to" (stranded, informal) | Yes |
When You Cannot Omit the Pronoun
1. When the pronoun is the subject of the relative clause
If nothing else separates the gap from the verb, the pronoun is doing subject duty and must be kept: The woman who runs the bakery is my neighbour. Dropping "who" here would leave "The woman runs the bakery is my neighbour," which is not a grammatical sentence.
2. In non-defining (non-restrictive) relative clauses
Clauses set off by commas simply add extra, non-essential information about something already fully identified, and the relative pronoun is never optional in this type of clause: My father, who is a teacher, called. You cannot say "My father, is a teacher, called" or "My father, teacher, called."
3. When the preposition comes before the relative pronoun (formal style)
In formal English, a preposition can be placed directly before the relative pronoun: the man to whom I spoke, the topic about which we disagreed. In this fronted, formal pattern the pronoun cannot be dropped. However, if you move the preposition to the end of the clause instead (the more common, everyday pattern), the pronoun becomes optional: the man (who/that) I spoke to, the topic (that) we disagreed about.
Style note: Contact clauses are extremely common in spoken English and informal writing — they sound natural and economical. In more formal or academic writing, keeping "that," "which" or "who" explicit is generally preferred and can sound clearer, especially in longer sentences.
Common Mistakes
-
Dropping the pronoun when it is the subject: This is the most frequent error.
Wrong: The man called is my uncle.
Correct: The man who called is my uncle. -
Dropping the pronoun in a non-defining clause: Commas signal that the pronoun is required.
Wrong: My sister, lives in Berlin, is visiting next week.
Correct: My sister, who lives in Berlin, is visiting next week. -
Dropping the pronoun after a fronted preposition: Formal "preposition + whom/which" cannot lose the pronoun.
Wrong: The client to I spoke was satisfied.
Correct: The client to whom I spoke was satisfied. (or, informally, the client I spoke to) -
Adding a second subject pronoun after dropping the object pronoun:
Wrong: The book I read it was excellent.
Correct: The book I read was excellent.
Practice Tips
Run the subject test: Before deciding whether to drop the pronoun, check what comes right after the gap. A noun/pronoun subject immediately after means the pronoun was the object — safe to drop. A verb immediately after means the pronoun was the subject — keep it.
- Rewrite pairs: Take sentences with "that/which/who" and try removing the pronoun; check whether the sentence still makes sense and means the same thing.
- Listen for contact clauses: In conversations, podcasts and films, notice how often speakers drop the pronoun in phrases like "the thing I told you about" or "the guy I met."
- Watch the commas: If a relative clause has commas around it, that's your signal the pronoun is non-negotiable.
Practice Exercises
Grammar Quiz
Decide whether the relative pronoun can be omitted in each sentence.
Complete the Sentence
Add "that/which/who" only where it is grammatically required.
True or False
Judge whether each contact clause is correctly formed.
Flash Cards
Drill subject vs. object relative pronouns.
Matching Pairs
Match full relative clauses to their contact-clause versions.
Unjumble
Reorder scrambled words into a correctly formed contact clause.
Practise Contact Clauses
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Frequently Asked Questions
What is a contact clause?
A contact clause is a defining relative clause in which the relative pronoun ("that," "which," "who" or "whom") has been omitted, so the main clause and the relative clause sit directly next to each other. For example, "The book I read was excellent" is a contact clause version of "The book that I read was excellent." Contact clauses are also called zero relative clauses.
When can I omit the relative pronoun?
You can omit the relative pronoun only when it functions as the object of the verb (or of a preposition) inside the relative clause, and the clause is defining (no commas). For example, in "The man (who) I met yesterday works here," "who" is the object of "met," so it can be dropped.
Why can't I say "The man called is my uncle"?
Because "who" in "The man who called is my uncle" is the subject of "called," it cannot be dropped. Removing it changes the sentence's structure: "The man called is my uncle" sounds like a reduced clause meaning "the man who was called," which is a different meaning altogether. The subject relative pronoun must always stay in place.
Can I drop the relative pronoun in non-defining relative clauses?
No. Non-defining (non-restrictive) relative clauses, the ones separated from the main clause by commas, always keep the relative pronoun because they add extra, non-essential information rather than identifying which noun is meant. For example, "My father, who is a teacher, called" cannot become "My father, is a teacher, called."
What happens when the relative pronoun is the object of a preposition?
It depends on where the preposition goes. In the formal pattern, where the preposition comes directly before the pronoun ("the man to whom I spoke"), the pronoun cannot be omitted. In the more common, informal pattern, where the preposition is left ("stranded") at the end of the clause ("the man I spoke to"), the pronoun can be omitted freely.
Are contact clauses formal or informal English?
Contact clauses are extremely common in spoken English and everyday informal writing because they sound natural and economical. In more formal or academic writing, many writers prefer to keep "that," "which" or "who" explicit, especially in longer or more complex sentences, since the full form can be clearer to read.
How can I quickly test whether a pronoun can be dropped?
Look at what comes immediately after the position where the pronoun would go. If a noun or pronoun subject (like "I," "she," "the boy") comes right after, the relative pronoun was acting as the object and can be dropped. If the verb comes immediately after with no subject in between, the relative pronoun was the subject of the clause and must be kept.
Is "whom" ever used in contact clauses?
"Whom" itself is always the object form, so when it is used informally at the end of a clause ("the man I spoke to") it is simply omitted along with "who." "Whom" only has to stay visible in the formal pattern where a preposition comes directly before it, e.g. "the man to whom I spoke," where dropping it is not possible.
What is the difference between "The song I heard" and "The song that was playing"?
In "The song (that) I heard on the radio," "that" is the object of "heard" (the subject is "I"), so it can be omitted. In "The song that was playing on the radio," "that" is the subject of "was playing" with no other subject present, so it cannot be omitted. Checking what follows the gap tells you immediately which rule applies.
At what level are contact clauses typically taught?
Contact clauses are usually introduced at B1 level alongside defining relative clauses, and refined further at B2 once learners also study non-defining clauses and formal preposition + relative pronoun patterns. Recognising and producing contact clauses correctly is an important marker of natural, fluent spoken and written English.