The relative pronoun is so called because it relates or refers to another word, called its antecedent, to which it joins the clause that it introduces. The relative pronouns are who, which, what, that; and the compound relatives are whoever, whosoever, whichever, whichsoever, whatever, whatsoever.
They are declined as follows:
Singular and Plural
| Nom. | who | which | whoever | whosoever |
| Poss. | whose | of which | whosever | whosesoever |
| Obj. | whom | which | whomever | whomsoever |
That, what, whichever, whichsoever, whatever, and whatsoever are not declined. They have the same form in the nominative and objective cases, and are not used in the possessive case.
What is peculiar in that it never has an antecedent expressed, but itself stands for both antecedent and relative. It is called the double relative. Compare the following:
| I did not hear the words that he said. |
| I did not hear that which he said. |
| I did not hear what he said. |
That is called the restrictive relative, because it limits or restricts its antecedent to the meaning expressed in the clause introduced by that. A restrictive clause is one, therefore, that is needed to make the meaning of the sentence clear. Compare the following:
Non-restrictive: John Brown, who has no disease, needs no physician.
Restrictive: He that hath no disease needs no physician.