119. The _gender_, _number_, and _person_ of the relatives _who_,
_which_, and _that_ must be determined by those of the antecedent; the
_case_ depends upon the function of the relative in its own clause.

For example, consider the following sentence:

"He uttered truths _that_ wrought upon and molded the lives of
those _who_ heard him."

Since the relatives hold the sentence together, we can, by taking them
out, let the sentence fall apart into three divisions: (1) "He uttered
truths;" (2) "The truths wrought upon and molded the lives of the
people;" (3) "These people heard him."

_That_ evidently refers to _truths_, consequently is neuter, third
person, plural number. _Who_ plainly stands for _those_ or _the
people_, either of which would be neuter, third person, plural number.
Here the relative agrees with its antecedent.

We cannot say the relative agrees with its antecedent in _case_.
_Truths_ in sentence (2), above, is subject of _wrought upon and
molded_; in (1), it is object of _uttered_. In (2), _people_ is the
object of the preposition _of_; in (3), it is subject of the verb
_heard_. Now, _that_ takes the case of _the truths_ in (2), not of
_truths_ which is expressed in the sentence: consequently _that_ is in
the nominative case. In the same way _who_, standing for _the people_
understood, subject of _heard_, is in the nominative case.

Exercise.