with. This results in seven classes: Single-gender masculine nouns (e.g., boy, stepson) Single-gender feminine nouns (e.g., girl, stepdaughter, actress) Single-gender neuter nouns (e.g., arrival, beer) Dual-gender masculine/feminine nouns (e.g., actor, doctor) Dual-gender masculine/neuter nouns (e.g., bull, brother) Dual-gender feminine/neuter nouns (e.g., cow, sister, ship) Triple-gender nouns (e.g., baby, dog) These classes are not equally common. For instance, single-gender neuter nouns account for a large majority of common nouns while dual-gender masculine/neuter nouns account for only male animal species and certain kinship terms that can apply to both humans and animals. In the relative pronoun subsystem, nouns can be classified according to whether they agree with who or which. Nouns that agree with who are called personal (or animate) nouns while nouns that agree with which are called non-personal (or inanimate) nouns. Though there is substantial overlap between nonpersonal nouns and neuter nouns and between personal nouns and masculine and feminine nouns, the overlaps are not perfect. For instance, a ship can agree with either it or she but can only agree with which (not who). Similarly, which can serve as an antecedent to he or she, as in there is a dog which attacked his/her owner. The syntax of nouns and noun phrases Some defining properties of English nouns are that they function as the heads of NPs and that they can be specified by determinatives and modified by pre-head adjective phrases. A defining property of English NPs is that they prototypically function at the clause level as subjects, objects, and predicative complements. Functions English nouns function as the head of a nominal (see §Internal structure below), which in turn mostly functions as the head of an NP. At the clause-level, English NPs typically function as subjects, objects, and predicative complements. The following table shows these typical functions and the other functions NPs can take: Nominals (see §Internal structure, below), also appear as pre-head modifier in a nominal (e.g., a two day conference). Internal structure A simple noun phrase like some good ideas has a head nominal, a phrase that excludes any determinative (here, some), and that nominal, in turn, has a head noun (here ideas) along with any modifiers or complements. Roughly speaking, the nominal includes everything after the determinative (similar to the way a clause has a verb phrase that includes basically everything after the subject). The following tree shows the internal structure of an NP with all