Structure: ‘Relative clauses’

What is a relative clause?

A relative clause adds information about a noun by joining it to a second idea, so you avoid writing two short, choppy sentences. It usually begins with a relative pronoun — who, which, that, whose — or a relative adverb such as where or when. When the regulator confirmed that it had cleared electric air taxis to fly, almost every sentence in the coverage leaned on them.

Relative clauses let writers pack precise detail into a single, flowing sentence — exactly the dense, information-rich style you meet in regulatory and industry reporting.

Defining and non-defining clauses

A defining clause identifies which thing we mean and takes no commas: the eight projects that will fly air taxis. A non-defining clause adds extra, non-essential detail and is fenced off with commas: Joby Aviation, which has invested billions of dollars, is one of the leading developers. Use that only in defining clauses; use which for non-defining ones.

Relative clauses with prepositions

At C1 level you will often move a preposition in front of the relative pronoun for a formal register: the framework under which operators may begin services, or the states in which the trials will run. The everyday spoken version pushes the preposition to the end (the framework which operators may begin services under), but the fronted form dominates written aviation English.

Reduced relative clauses

When the clause is defining and contains a passive idea, you can often delete the relative pronoun and the verb be: the data that is gathered during the trials becomes the data gathered during the trials. This shortened form keeps the tight, professional rhythm of airworthiness and certification writing.

Try these

Combine each pair into one sentence using the relative structure cued in brackets. Then reveal the model answers.

1. The FAA has selected eight projects. They will operate electric air taxis. (that)
2. Joby Aviation has invested billions of dollars. It is one of the leading eVTOL developers. (which — non-defining)
3. A vertiport is a ground facility. eVTOL aircraft take off and land there. (where)
4. The programme creates a framework. Operators may begin commercial services under it. (preposition + which)
5. EASA is developing a rival pathway. Its regulators want to set the global standard. (whose)
6. The data will shape the permanent rules. It is gathered during the trials. (reduced relative)

CEFR Level C1 / ICAO Level 6

Once you can build relative clauses comfortably, see how they collapse into participle clauses — a participle clause is usually just a defining relative clause with the pronoun and be removed.