There are two basic classes of nouns in Italian, referred to as genders, masculine and feminine. Gender may be natural ("ragazzo" 'boy', "ragazza" 'girl') or simply grammatical with no possible reference to biological gender (masculine "costo" 'cost', feminine "costa" 'coast'). Masculine nouns typically end in "-o" ("ragazzo" 'boy'), with plural marked by "-i" ("ragazzi" 'boys'), and feminine nouns typically end in "-a", with plural marked by "-e" ("ragazza" 'girl', "ragazze" 'girls'). For a group composed of boys and girls, "ragazzi" is the plural, suggesting that "-i" is a general plural. A third category of nouns is unmarked for gender, ending in "-e" in the singular and "-i" in the plural: "legge" 'law, f. sg.', "leggi" 'laws, f. pl.'; "fiume" 'river, m. sg.', "fiumi" 'rivers, m. pl.', thus assignment of gender is arbitrary in terms of form, enough so that terms may be identical but of distinct genders: "fine" meaning 'aim', 'purpose' is masculine, while "fine" meaning 'end, ending' (e.g. of a movie) is feminine, and both are "fini" in the plural, a clear instance of "-i" as a non-gendered default plural marker. These nouns often, but not always, denote inanimates. There are a number of nouns that have a masculine singular and a feminine plural, most commonly of the pattern m. sg. "-o", f. pl. "-a" ("miglio" 'mile, m. sg.', "miglia" 'miles, f. pl.'; "paio" 'pair, m. sg., "paia" 'pairs, f. pl.'), and thus are sometimes considered neuter (these are usually derived from neuter Latin nouns). An instance of neuter gender also exists in pronouns of the third person singular.