+373.+ We are sometimes confused as to which relative pronoun to use in
introducing an adjective clause. We hesitate as to whether we should use
_that_ or _who_ or _which_. Remember that _who_ always refers to
_persons_, _which_ refers to _animals_ or _things_, and _that_ may refer
to either _persons_, _animals_ or _things_.
So when referring to a _person_, we may use either _who_ or _that_, and
when referring to _animals_ or _things_, we may use either _which_ or
_that_. As, for example, we may say, either, _The man who was here
yesterday came back today_, or _The man that was here yesterday came
back today_. Either is correct, for _who_ and _that_ both refer to
persons.
+374.+ We may make a little distinction in the use of _who_ and _that_
when referring to _persons_, however. A clause introduced by _that_ is
usually a restrictive clause. It limits or restricts the meaning of the
noun which it modifies. When you say, _The man that was here yesterday_,
you mean _that_ man and no other, limiting your meaning to that
particular man. On the other hand, when you say, _The man who was here
yesterday_, there is no restriction or limitation expressed in the use
of the clause, but it is merely a descriptive clause, adding a new fact
to our knowledge concerning that particular man.
The same is true when we are speaking of _things_ using either _that_ or
_which_. The clause introduced by _which_ is presumably a descriptive
clause. We do, however, often use _who_ or _which_ when the sense of the
clause is restrictive, but we should never use _that_ to introduce an
adjective clause, unless the sense is restrictive. When in your
sentences you can use, instead of the relative pronoun _who_ or _which_,
the conjunction _and_, you can know that the use of the pronoun _who_ or
_which_ is correct. As, for example: