Relative Clause

A relative clause is a subordinate clause that modifies a noun phrase, most commonly a noun. For example, the phrase "the man who wasn't there" contains the noun man, which is modified by the relative clause who wasn't there. A relative clause can also modify a pronoun, as in "he to whom I have written", or a noun phrase which already contains a modifier, as in "the black panther in the tree, which is about to pounce". The complete phrase (modified noun phrase plus modifying relative clause) is also a noun phrase.In many European languages, relative clauses are introduced by a special class of pronouns called relative pronouns; in the previous example, who is a relative pronoun. In other languages, relative clauses may be marked in different ways: they may be introduced by a special class of conjunctions called relativizers; the main verb of the relative clause may appear in a special morphological variant; or a relative clause may be indicated by word order alone. In some languages, more than one of these mechanisms may be possible.

Accessibility hierarchy

The antecedent of the relative clause (that is, the noun that is modified by it) can in theory be the subject of the main clause, or its object, or any other verb argument. In many languages, however, especially rigidly left-branching, dependent-marking languages with prenominal relative clauses, there are major restrictions on the role the antecedent may have in the relative clause.According to the classic study of Bernard Comrie, noun phrases can be ranked in the following order from most accessible to least accessible:

1. Nominative or absolutive
2. Accusative or ergative
3. Indirect object (e.g., "the man to whom I have written")
4. Oblique (adpositional) object (e.g., "the machine into which I put the coin")
5. Genitive (e.g., "the woman whose daughter is ill")
6. Comparative object (e.g., "the boy than whom I am smaller")

If a language can relativise positions lower in the accessibility hierarchy, it can always relativise positions higher up, but not vice versa. For example, Malagasy can relativise only subject and Chukchi only absolutive arguments, whilst Basque can relativise absolutives, ergatives and indirect objects, but not obliques or genitives or objects of comparatives.Languages which cannot relativise directly on noun phrases low in the accessibility hierarchy can sometimes use alternative voices to "raise" the relevant noun phrase so that it can be relativised. The most common example is the use of applicative voices to relativise obliques, but in such languages as Chukchi antipassives are used to raise ergative arguments to absolutive.

Major types of relative clause
Across the world's languages, linguists have identified four major types of relative clause. These are typically listed in order of the degree to which the role of the antecedent in the relative clause is represented as follows:

1. Gap strategy or gapped relative clause
2. Relative pronoun
3. Pronoun retention
4. Nonreduction

Examples
As regards relative clauses, English has two particularities that are unique among the Germanic languages:

1. In other Germanic languages, if a relative pronoun is the object of a preposition in the relative clause, then the preposition always appears at the start of the clause, before the relative pronoun. In English, the preposition will often appear where it would appear if the clause were an independent clause — in other words, the relative pronoun "strands" it when it moves to the start of the clause. It used to be common to regard this as a grammatical error (see: linguistic prescription) but in fact it has been a standard feature of the language since the times of Middle English.
2. In other Germanic languages, a relative pronoun is always necessary. In English, however, it may be suppressed in a restrictive clause (as in "The man we met was very friendly"), provided it would not serve as the subject of the main verb. When this is done, if in the unsuppressed counterpart the relative pronoun is the object of a preposition in the relative clause, then said preposition is always "stranded" in the manner described above; it is never moved to the start of the clause.

SUMBER : http://en.wikipedia.org/wiki/Relative_clause