A reduced relative clause is a shorter form of a full relative clause. Instead of who is, which was, or that are followed by a verb, the clause keeps only the participle or adjective — directly after the noun it describes.
The meaning stays the same. The sentence becomes tighter and more natural, especially in written English and formal speech.
How reduction works
A full relative clause typically contains three parts: a relative pronoun (who, which, that), a form of be (is, was, are, were), and a participle or adjective. Reduction removes the pronoun and the auxiliary, leaving the participle directly attached to the noun.
This works because the participle alone already tells the reader whether the action is active or passive. An -ing form signals that the noun is doing the action. A past participle signals that the noun is receiving it.
Active reduction: present participle
When the full relative clause describes an active, ongoing, or habitual action, the reduced form uses the -ing participle.
The last example shows an important point: the full clause does not have to be in a continuous tense. The road that connects is present simple, yet it reduces naturally to the road connecting. What matters is that the subject of the clause is the one performing the action.
Negation
To negate a reduced active clause, place not before the participle.
Passive reduction: past participle
When the full clause is passive — the noun is receiving the action — the reduced form uses the past participle (the third form of the verb: written, built, designed, taken).
Continuous passive: *being* + past participle
If the full clause uses a continuous passive (is being built, was being repaired), the reduced form keeps being.
This form appears mostly in formal or technical writing.
Reduction to an adjective
Sometimes the full relative clause contains only who/which/that + a form of be + an adjective. In this case, the adjective moves directly after the noun — no participle needed.
Not every adjective works in this position. It is most natural with adjectives like present, available, responsible, remaining, involved, concerned, visible.
When reduction is possible
Three conditions must be met for a relative clause to reduce cleanly.
1. The relative pronoun must be the subject of the clause.
If the pronoun is the object, reduction to a participle is not possible.
Compare with:
2. There must be a form of be to remove, or the verb must convert naturally to an -ing form.
Clauses with be + participle reduce most smoothly: just delete the pronoun and be.
Clauses in simple tenses without be can still reduce if the -ing form sounds natural:
But not every verb converts smoothly. The man who lives next door can become the man living next door in most contexts, but it may feel less natural than the full form in casual speech.
3. The reduced form must remain unambiguous.
If removing the relative pronoun creates confusion about which noun the participle modifies, keep the full clause.
Defining vs. non-defining
Both defining and non-defining relative clauses can be reduced. Non-defining clauses keep their commas.
Prepositional phrases as reduction
A special case of reduction: when the full clause contains only who/which/that + be + a prepositional phrase, removing the pronoun and be leaves just the phrase.
This is so common in everyday English that most speakers do not even think of it as a reduced clause — but structurally, it follows the same logic.
Common mistakes
Reducing object clauses
Forgetting being in continuous passives
Wrong participle form
Dangling participle (attaching to the wrong noun)