A pro-drop language (from "pronoun-dropping") is a language where certain classes of pronouns may be omitted when they can be pragmatically or grammatically inferable. The precise conditions vary from language to language, and can be quite intricate. The phenomenon of "pronoun-dropping" is part of the larger topic of zero or null anaphora. The connection between pro-drop languages, and null anaphora relates to the fact that a dropped pronoun has referential properties, and so is crucially not a null dummy pronoun. Pro-drop is licensed only in languages that have a positive setting of the pro-drop parameter, which allows the null element to be identified by its governor. Pro-drop is a problem when translating to a non-pro-drop language such as English, which requires the pronoun to be added, especially noticeable in machine translation. Amongst other reasons, it can also pose a problem with respect to transfer errors and second language acquisition. An areal feature of many northern European languages is that pronoun dropping is not, or seldom, possible (see Standard Average European); this is the case for English, French, German, and Emilian, among others. In contrast, Japanese, Mandarin Chinese, Slavic languages, Finno-Ugric languages, and Hebrew exhibit frequent pro-drop features. Some languages, such as Hindi, Greek, and European Portuguese, have the ability to pro-drop any argument. History of the term The term "pro-drop" stems from Noam Chomsky's "Lectures on Government and Binding" from 1981 as a cluster of properties of which "null subject" was one (for the occurrence of pro as a predicate rather than a subject in sentences with the copula see Moro 1997). Thus, a one-way correlation was suggested between inflectional agreement (AGR) and empty pronouns on the one hand and between no agreement and overt pronouns, on the other. In the classical version, languages which not only lack agreement morphology but also allow extensive dropping of pronouns—such as Japanese, Chinese, Korean, and Vietnamese—are not included, as is made clear in a footnote: "The principle suggested is fairly general, but does not apply to such languages as Japanese in which pronouns can be missing much more freely." (Chomsky 1981:284, fn 47). The term pro-drop is also used in other frameworks in generative grammar, such as in lexical functional grammar (LFG), but in a more general sense: "Pro-drop is a widespread linguistic phenomenon in which, under certain conditions, a structural NP may be unexpressed, giving rise to a pronominal interpretation." (Bresnan 1982:384).