High Quality Content by WIKIPEDIA articles! Relative clauses in the English language are formed principally by means of relative pronouns. The basic relative pronouns are who, which, and that (who also has the derived forms whom and whose). Various grammatical and stylistic rules exist for determining which of the relative pronouns can be used in a given instance. In some cases (as in "This is the man I saw"), it is possible to omit the relative pronoun entirely.