Restrictive clauses include information that are essential for the purpose of the sentence. Without these the sentence may not make sense or convey the intended meaning. That is, the clause restricts (makes specific) whatever it refers to. The clause follows who, which or that.
For example –
· The pen which you have broken was mine.
· The woman who came with us is my neighbour.
As opposed to restrictive clause, non-restrictive clause is not critical to the sentence, but additional information without which the sentence would still be meaningful and convey the message of the sentence. Non-restrictive start and end with commas to indicate that the information within the commas is optional (non-essential).
Like we have seen, the information between the commas is not essential to identify the rest of the sentence that follows, and can be easily removed. “My favourite chocolate cake is unavailable today” makes the same impact as “My favourite chocolate cake, which we ordered for my birthday, is unavailable today.”
A simple case
My sister, who was the college topper, hasn’t got a job yet.
The girl who was the college topper hasn’t got a job yet.
Notice the difference. Since we are talking about the ‘girl’, it could be anyone. So, the clause “who was the college topper” becomes essential to identify the noun (girl), hence it becomes a restrictive clause.
A quick trick to differentiate restrictive from non-restrictive clause is to put the clause in brackets or omit it and then read the sentence. If the sentence still conveys the information that it is supposed to, then the clause in question is a non-restrictive one.