Importance of Commas in Relative Clauses
English Grammar Index
Importance of Commas in Relative Clauses :
The passengers who had visas had no trouble at the frontier.
Who had visas is a defining relative clause which defines or limits its noun PASSENGERS.
The sentence implies that some passengers had visas, but some had not. Those without visas had trouble at the frontier.
Note how the meaning changes if we add commas.
The passengers, who had visas, had no trouble at the frontier.
This means that all the passengers had visas and therefore none of them had trouble. Who had visas, is a non – defining clause, which merely adds some information to the preceding noun.
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