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He chased two police community support officers (PCSOs) before being detained, the force said.

I saw the above at https://www.bbc.co.uk/news/uk-england-50014205

I know that the preposition are followed by a noun or noun phrases so

"Being detained" must be a noun. I still don't get it the role of "being" here.

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It is a so-called "gerund". I expect you are OK with "Please wash your hands before eating", yes? Your sentence is the same idea, except that the gerund (participle) is passive rather than active: He didn't himself detain anyone -- he was detained (by the police).

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Before being detained is a clause equivalent or a reduced clause. The complete version with a finite verb would be: He chased two police community support officers (PCSOs) before he was detained, the force said. In the reduced version, 'he' has been left out and as 'before' is a preposition, it requires the gerund of a verb that follows it. The gerund of the passive auxiliary 'be' is 'being'.

CB

Cross-posted

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Jigneshbharati

He chased two police community support officers (PCSOs) before being detained, the force said. I know that the preposition are followed by a noun or noun phrases so "Being detained" must be a noun. I still don't get it the role of "being" here.

No: it's not a noun, but a non-finite clause with the verb "being" as predicator, i.e. head of the clause with "detained" as its clausal complement. In addition to NPs, prepositions can take quite a wide range of complements, including clauses both finite and, as here, non-finite.

In your example, the gerund-participial clause "being detained" is complement of the preposition "before", and is the non-finite equivalent of the finite "he was detained". Non-finite clauses are often preferred when the matrix subject is the same as the subordinate one. They are also a little less wordy.

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Super! Thanks a lot BillJ.