In linguistics, a zero or null is a segment which is not pronounced or written. It is a useful concept in analysis, indicating lack of an element where one might be expected. It is usually written with the symbol "∅", in Unicode . A common ad hoc solution is to use the Scandinavian capital letter Ø instead. There are several kinds of zero: In phonetics, a null phoneme or zero phone indicates that no phone is produced where one might be expected. For example, in syllable structure analysis, null onset indicates that a syllable lacks an initial consonant (onset) that is normally required by phonotactics of the considered language. For an example, see Standard Chinese phonology#Zero onset. In morphology, a zero morph, consisting of no phonetic form, is an allomorph of a morpheme that is otherwise realized in speech. In the phrase two sheep-∅, the plural marker is a zero morph (see nouns with identical singular and plural forms), which is an allomorph of -s as in two cows. In the phrase I like-∅ it, the verb conjugation has a zero affix, as opposed to the third-person singular present -s in he likes it. In grammar, a zero pronoun occurs in some languages. In the English sentence nobody knows ∅ the zero pronoun plays the role of the object of the verb, and in ∅ makes no difference it plays the role of the subject. Likewise, the zero pronoun in the book ∅ I am reading plays the role of the relative pronoun that in the book that I am reading. In generative grammar, this is also referred to as PRO. In pronoun-dropping languages, including null subject languages such as most Romance languages, the zero pronoun is a prominent feature. A zero subordinate conjunction occurs in English in sentences like I know ∅ he likes me, in which the zero conjunction plays the role of the subordinate conjunction that in I know that he likes me. This comes naturally to native speakers of English, but non-native learners have to consciously adjust to it, as it rarely occurs in other languages. A zero article is an unrealized indefinite or definite article in some languages, such as the plural indefinite article in English. A zero copula, in which a copula such as the verb to be is implied but absent. For example, in Russian the copula is usually omitted in the present