In this chapter I will examine a number of possible linguistic factors which affect the realization of the relative marker (i.e. either as WH, TH or ∅):

1. type of clause – restrictive or non-restrictive

2. features or characteristics of the antecedent/head NP – animateness, definiteness, type of noun modification structure, e.g. determiner, quantifier, superlative

3. syntactic position/grammatical function of the relative in S2, the relative clause – subject, object, indirect object, predicate nominative, temporal, locative, stranded and shifted prepositions and genitive

Type of clause

Most grammars of English, whether prescriptive or descriptive, recognize at least two types of relative clauses: restrictive and non-restrictive. This distinction is made on the basis of the way in which the head NP or antecedent is modified by the relative clause. A restrictive clause further limits the head NP's reference, while a non-restrictive clause adds only additional information to a head which is already independently identified, or is unique in its reference and has no need of further modification to identify its referent. Classic examples of each type are:

1. (1) The girl who lives next door to me. (restrictive)

2. (2) Mary Smith, who lives next door to me. (non-restrictive)

Proper names constitute a class of unique referents because their identity is the same no matter what else may follow after. In the case of possible ‘mistaken identity’ though, proper names may occur with restrictive clauses, e.g. where there is clearly more than one person with the same name. In the following example, the use of the definite article also adds to this interpretation (cf. also Lyons 1977: ch. 7).

1. (3) The Mary Smith that I know lives next door.