RELATIVE PRONOUNS.
I. RESTRICTIVE AND UNRESTRICTIVE RELATIVES.
What these terms mean.
412. As to their conjunctive use, the definite relatives who, which, and that may be coördinating or restrictive.
A relative, when coördinating, or unrestrictive, is equivalent to a conjunction (and, but, because, etc.) and a personal pronoun. It adds a new statement to what precedes, that being considered already clear; as, "I gave it to the beggar, who went away." This means, "I gave it to the beggar [we know which one], and he went away."
A relative, when restrictive, introduces a clause to limit and make clear some preceding word. The clause is restricted to the antecedent, and does not add a new statement; it merely couples a thought necessary to define the antecedent: as, "I gave it to a beggar who stood at the gate." It defines beggar.
413. It is sometimes contended that who and which should always be coördinating, and that always restrictive; but, according to the practice of every modern writer, the usage must be stated as follows:—
A loose rule the only one to be formulated.
Who and which are either coördinating or restrictive, the taste of the writer and regard for euphony being the guide.
That is in most cases restrictive, the coördinating use not being often found among careful writers.