2. Relative Pronouns in Non-Restrictive Clauses Non-restrictive clauses are placed after nouns which are more or less definite in meaning. They merely add some more information about such nouns. Unlike restrictive clauses, they are not essential in the sentence and can be omitted without causing confusion. Also unlike restrictive clauses, they are separated from their noun by commas. This construction is fairly formal and more common in written than in spoken English.
Only who can be used for persons in-such clauses.
Tom, who is incurably romantic, has just got engaged for the fourth time.
The objective form whom must always be used and cannot be omitted.
My uncle Jim, whom I haven't seen for years, is coming home next week.
The preposition is normally placed before whom, though it is possible in conversation to use who and move the preposition to the end of the clause.
Mr Pitt, for whom I am canvassing, is a most estimable candidate.
The pronoun whichmust always be used for things, and it cannot,be omitted.
His old ear, which breaks down every few miles, is dearer to him than his wife.
The preposition is normally placed before which.
Hampton Court, to which he took me on Saturday, has a wonderful maze. B u t: Your inefficiency, which I have put up with since you came to this office, is beginning to be unbearable.
Thus which is placed immediately after its noun and follow-ed by the clause if the predicate of the clause is expressed by such verb-adverb groups as give up, look forward to, put up with, etc...
The relative which can also be used to refer to a whole clause.
He hit the dog, which was a stupid thing to do. I had to have my ear filled, which held me up.
The possessive whosemay be used for people, animals and things; of which is, however, more common for things than whose.
My dog, whose temper is very uncertain, often bites the judges at dog shows. She wore a bunch of cyclamen, whose scent she was very fond of. His thesis, of which the last hundred pages are absolute .nonsense, will, probably win him a lot of notoriety.
N o t e. Such constructions should be avoided wherever possible, and it would be more usual to say:
My dog has a very uncertain temper and often bites the judges at dog shows. His thesis will probably win him a lot of notoriety because the last hundred pages are absolute nonsense.