preposition, adverb or conjuntion

Dear teachers,

Would you please give me a hint about how to recognize a preposition from an adverb from a conjunction ?

In the following sentence how can I know if "before" is a preposition or an adverb (and sometimes a conjunction) ?
A conjunction always introduces a clause ?

Before the Fire, there had been a plague, the like of which had not been known before."

Thanks
Hela

Yes, a (subordinating) conjunction always introduces a clause, and so that clearly rules it out as a choice in the sentence you cite.
Where the word 'before' is followed simply by a noun phrase (as is the first 'before' in the same sentence), it is a preposition, and where it is followed by nothing at all (as the second), it is an adverb.

Quote:

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Originally Posted by hela

Dear teachers,

Would you please give me a hint about how to recognize a preposition from an adverb from a conjunction ?

In the following sentence how can I know if "before" is a preposition or an adverb (and sometimes a conjunction) ?
A conjunction always introduces a clause ?

Before the Fire, there had been a plague, the like of which had not been known before."

Thanks
Hela

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Thank you :-)