Relative Clauses

Relative clauses are subordinate clauses that modify a noun phrase, introduced by a relative pronoun (who, which, that, whose, whom) or relative adverb (where, when, why). They are one of the most heavily taught structures in ELT and one of the most persistent areas of L2 difficulty.

Defining vs Non-defining

Type	Function	Punctuation	Example
Defining (restrictive)	Identifies which noun is meant; essential information	No commas	The student who passed got a certificate.
Non-defining (non-restrictive)	Adds extra information; removable	Commas	My brother, who lives in Hanoi, is a teacher.

Key differences:

• That can replace who/which in defining clauses but never in non-defining ones
• The relative pronoun can be omitted in defining object clauses: The book (that) I read
• Non-defining clauses cannot modify indefinite pronouns: *Someone, who I met is ungrammatical

Types by Grammatical Role

The relative pronoun can function as subject, object, or possessive within the relative clause:

• Subject: The woman who called is my neighbour. (who = subject of called)
• Object: The film (that) we watched was excellent. (that = object of watched)
• Possessive: The teacher whose class I attended was inspiring.
• Prepositional: The house in which she lived / which she lived in

Processing Difficulty

Research consistently shows a hierarchy of difficulty for L2 learners (Keenan and Comrie, 1977: Noun Phrase Accessibility Hierarchy):

Subject > Direct Object > Indirect Object > Oblique > Genitive > Object of Comparison

Subject relatives are easiest; each step down the hierarchy is harder. Object relative clauses where the relative pronoun is omitted (The man I saw) are particularly challenging because the surface form gives no explicit signal of the relativisation.

Common L2 Errors

• Resumptive pronouns: The man who I saw him, inserting a pronoun that duplicates the relative pronoun's role. Common in learners whose L1 uses this strategy (Arabic, Vietnamese, Chinese)
• Avoidance: learners may avoid relative clauses altogether, preferring coordination (I met a man. He was very tall.), a well-documented strategy (Schachter, 1974)
• That/which confusion: overgeneralising that to non-defining clauses or vice versa
• Preposition placement: uncertainty between in which and which...in

Reduced Relative Clauses

In academic and formal writing, relative clauses are frequently reduced to participial phrases:

• The results which were obtained from... → The results obtained from...
• Students who are studying abroad... → Students studying abroad...

This reduction is characteristic of high Lexical Density academic prose and is essential for reading comprehension at advanced levels.