Relative Pronouns

Relative Pronouns are the pronouns used to introduce relative clauses. In English, who (with its forms: whom & whose), which, that, what can be used as relative pronouns. Often, the relative pronoun has an antecedent, i.e. a noun it refers to. In this case, the relative clause provides a characterization or specification of this noun. For example, Here is the book, which he has written. 

Sometimes there is no specific antecedent, then the whole relative clause functions as a noun. For example, What he has written, is here. Sometimes the antecedent is general. For example, The thing, he has written, is here

In Greek a Relative Pronoun is a pronoun, hence in changes in Gender, Number, and Case. The Gender and Number are determined by the antecedent. The Case is determined by the function of the Relative Pronoun in the relative clause. 

For example, the translation of the sentence Here is the book, which he has written in Greek, is as follows: ὧδε ἔστιν τὸ βιβλίον ὃ γέγραφεν

Both What he has written, is here and The thing, he has written, is here can be rendered in Greek as follows: ὃ γέγραφεν ὧδε ἔστιν

Here are the forms of the Relative Pronouns: