A pro-drop language (from "pronoun-dropping") is a
language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign language) and writing. Most languages have a writing system composed of glyphs to inscribe the original soun ...
in which certain classes of
pronoun In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. The traditional areas of linguistic analysis include ...

s may be omitted when they are pragmatically or grammatically inferable. The precise conditions vary from language to language, and can be quite intricate. The phenomenon of "pronoun-dropping" is also commonly referred to as zero or null anaphora. In the case of pro-drop languages, null anaphora refers to the fact that the null position has referential properties, meaning it is not a null dummy pronoun. Pro-drop is only licensed in languages that have a positive setting of the pro-drop parameter, which allows the null element to be identified by its governor. In pro-drop languages with a highly inflected verbal morphology, the expression of the subject pronoun is considered unnecessary because the verbal inflection indicates the person and number of the subject, thus the referent of the null subject can be inferred from the grammatical inflection on the verb. Even though in everyday speech there are instances when who or what is being referred to can be inferred from context, non-pro-drop languages still require the pronoun. However, pro-drop languages allow those referential pronouns to be omitted, or be phonologically null. Among major languages, some which might be called pro-drop languages are
Korean Korean may refer to: People and culture * Koreans, an ethnic group originating in the Korean Peninsula * Korean cuisine * Korean culture * Korean language * Korean alphabet, or Hangul Places * Korean Peninsula, a peninsula in East Asia * Korea, ...
Hindi Hindi ( Devanagari: हिन्दी, IAST/ ISO 15919: ''Hindī''), or more precisely Modern Standard Hindi ( Devanagari: मानक हिन्दी, IAST/ ISO 15919: ''Mānak Hindī''), is an Indo-Aryan language spoken chiefly in ...
(featuring pronoun deletion not only for subjects, but for practically all grammatical contexts). South Asian languages such as
Hindi Hindi ( Devanagari: हिन्दी, IAST/ ISO 15919: ''Hindī''), or more precisely Modern Standard Hindi ( Devanagari: मानक हिन्दी, IAST/ ISO 15919: ''Mānak Hindī''), is an Indo-Aryan language spoken chiefly in ...
, in general, have the ability to pro-drop any and all arguments. Chinese,
Slavic languages The Slavic languages, also known as the Slavonic languages, are Indo-European languages The Indo-European languages are a language family native to western and southern Eurasia. It comprises most of the languages of Europe together with t ...
, American Sign Language and Vietnamese also exhibit frequent pro-drop features. In contrast, non-pro-drop is an areal feature of many northern European languages (see Standard Average European), including French, (standard) German, English and Emilian. Some languages might be considered partially pro-drop in that they allow deletion of the subject pronoun. These Null-subject language, null-subject languages include most Romance languages (French language, French is an exception) as well as all the Balto-Slavic languages. Colloquial and German dialects, dialectal German, unlike the standard language, are also partially pro-drop; they typically allow deletion of the subject pronoun in main clauses without inversion (linguistics), inversion, but not otherwise. Hungarian allows deletion of both the subject and object pronouns.

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 (grammar), predicate rather than a subject (grammar), subject in sentences with the copula (linguistics), copula see Moro 1997). Thus, a one-way correlation was suggested between agreement (linguistics), 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). The empty category assumed (under government and binding theory) to be present in the vacant subject position left by pro-dropping is known as ''pro'', or as "little pro" (to distinguish it from "big PRO", an empty category associated with non-finite verb phrases).



Consider the following examples from Japanese: : :''Kono kēki wa oishii. Dare ga yaita no?'' :This cake TOPIC tasty-PRESENT. Who SUBJECT bake-PAST EXPLAIN.? :"This cake is tasty. Who baked it?" : :''Shiranai. Ki ni itta?'' :know-NEGATIVE. like-PAST? :"I don't know. Did you like it?" The words in bold in the English translations (''it'' in the first line; ''I'', ''you'', and ''it'' in the second) appear nowhere in the Japanese sentences but are understood from context. If nouns or pronouns were supplied, the resulting sentences would be grammatically correct but sound unnatural. (Learners of Japanese as a second language, especially those whose first language is non-pro-drop like English or French, often supply personal pronouns where they are pragmatically inferable, an example of language transfer.)


The above-mentioned examples from Japanese are readily rendered into Chinese: : :''Zhè kuài dàngāo hěn hǎochī. Sheí kǎo de?'' :This piece cake DEGREE tasty. Who bake-MODIFY? :"This cake is tasty. Who baked it?" : :''Bù zhīdào. Xǐhuan ma?'' :Not know. like QUESTION-YES/NO? :"I don't know. Do you like it?" Unlike in Japanese, the inclusion of the dropped pronouns does not make the sentence sound unnatural.


Hindi Hindi ( Devanagari: हिन्दी, IAST/ ISO 15919: ''Hindī''), or more precisely Modern Standard Hindi ( Devanagari: मानक हिन्दी, IAST/ ISO 15919: ''Mānak Hindī''), is an Indo-Aryan language spoken chiefly in ...
shows radical pro-drop. This type of pro-drop differs from pro-drop in languages like Spanish where pro-drop is licensed by rich verbal morphology. South Asian languages such as
Hindi Hindi ( Devanagari: हिन्दी, IAST/ ISO 15919: ''Hindī''), or more precisely Modern Standard Hindi ( Devanagari: मानक हिन्दी, IAST/ ISO 15919: ''Mānak Hindī''), is an Indo-Aryan language spoken chiefly in ...
, in general, have the ability to pro-drop any and all arguments. Hindi is a Split ergativity, split-ergative language and when the subject of the sentence is in the ergative case (also when the sentence involves the infinitive participle, which requires the subject to be in the dative caseBhatt, Rajesh (2003). Experiencer subjects. Handout from MIT course “Structure of the Modern Indo-Aryan Languages”.), the verb of the sentence agrees in gender and number with the object of the sentence, hence making it possible to drop the object since it can be contextually inferred from the gender of the verb. In the example below, the subject is in the ergative case and the verb agrees in Grammatical number, number and Grammatical gender, gender with the direct object. In the example below, the subject is in the dative case and the verb agrees in Grammatical number, number and Grammatical gender, gender with the direct object. In the example below, the subject is in the nominative case and the verb agrees in Grammatical number, number, Grammatical gender, gender, and also in Grammatical person, person with the subject.


Arabic is considered a null-subject language, as demonstrated by the following example: :ساعد غيرك، يساعدك :''sāʻid ghayrak, yusāʻiduk.'' :Help other, help.PST.3SG you. :If you help another, he helps you.


:''Sen-i gör-dü-m'' :2SG-accusative_case, ACC see-past_tense, PST-1SG :I saw you. The subject "I" above is easily inferable as the verb ''gör-mek'' "to see" is conjugated in the first person simple past tense form. The object is indicated by the pronoun ''seni'' in this case. Strictly speaking, pronominal objects are generally explicitly indicated, although frequently possessive suffixes indicate the equivalent of an object in English, as in the following sentence. :''Gel-diğ-im-i gör-dü-n mü?'' :come-nominalisation, NMLZ-possessive, POS.1SG-accusative_case, ACC see-past_tense, PST-2SG question, Q :Did you see me coming? In this sentence, the object of the verb is actually the action of coming performed by the speaker (''geldiğimi'' "my coming"), but the object in the English sentence, "me", is indicated here by the possessive suffix ''-im'' "my" on the nominalised verb. Both pronouns can be explicitly indicated in the sentence for purposes of emphasis, as follows: :''Sen ben-im gel-diğ-im-i gör-dü-n mü?'' :2SG 1SG-POSS come-"ing"-possessive, POS.1SG-accusative_case, ACC see-past_tense, PST-2SG question, Q :Did ''you'' see ''me'' coming?


In Swahili, both subject and object pronouns can be omitted as they are indicated by verbal prefixes. :''Ni-ta-ku-saidia.'' :''SUBJ.1SG-future_tense, FUT-OBJ.2SG-help :I will help you.


English is not a pro-drop language. Nonetheless, subject pronouns are almost always dropped in imperative sentences (e.g., ''Come here''), with the subject "you" understood or communicated non-verbally. In informal speech, the pronominal subject is sometimes dropped. This ellipsis has been called "conversational deletion" and "left-edge deletion", and is common in informal spoken English as well as certain linguistic register, registers of written English, notably diaries. Most commonly, it is the first person singular subject which is dropped. Some other words, especially Copula (linguistics), copulas and Auxiliary verb, auxiliaries, can also be dropped. *''[Have you] ever been there?'' *''[I'm] going to the shops. [Do you] want to come?'' *''[I] haven't been there yet. [I'm] going later.'' *Seen on signs: ''[I am/We are] out to lunch; [I/we will be] back at 1:00 [P.M].'' *''What do you think [of it]?'' – ''I like [it]!'' (the latter only in some dialects and registers) *''[Do you] want a piece of cake?'' In speech, when pronouns are not dropped, they are more often relaxed pronunciation, reduced than other words in an utterance. Relative pronouns, provided they are not the subject, are often dropped in short restrictive clauses: ''That's the man [whom] I saw.'' The dropping of pronouns is generally restricted to very informal speech and certain fixed expressions, and the rules for their use are complex and vary among dialects and registers. A noted instance was the "lived the dream" section of George H. W. Bush's speech at the 1988 Republican National Convention.

Null-subject languages

Modern Greek

Subject pronouns are usually omitted in modern Greek language, Greek, though the verb is inflected for person and number. Example: :''Βλέπεις εκείνο το κούτσουρο; Θα ήταν καλό για τη φωτιά. Είναι τελείως ξερό.'' :See that the log? Would be good for the fire. Is completely dried ''(literal, direct translation)'' :(Do) you see this log? It would be good for the fire. It has completely dried. ''(idiomatic translation)''

Romance languages

Most Romance languages (with the notable exception of French) are categorised as pro-drop as well, though generally only in the case of subject pronouns. Unlike in Japanese, however, the missing subject pronoun is not inferred strictly from pragmatics, but partially indicated by the morphology (linguistics), morphology of the verb, which inflects for person and number of the subject.


In Spanish, the verb is inflected for both person and number, thus expression of the pronoun is unnecessary because it is grammatically redundant. In the following example, the inflection on the verb ''ver,'' 'see', signals informal 2nd person singular, thus the pronoun is dropped. Similarly, from both the context and verbal morphology, the listener can infer that the second two utterances are referring to the log, so the speaker omits the pronoun that would appear in English as "it." :''¿Ves este tronco? Sería bueno para la fogata. Está completamente seco.'' (Spanish) :See this log? Would be good for the campfire. Is completely dry ''(literal, direct translation)'' :(Do) you see this log? It would be good for the campfire. It is completely dry ''(English gloss)'' Although Spanish is predominantly a pro-drop language, not all grammatical contexts allow for a null pronoun. There are some environments that require an overt pronoun. In contrast, there are also grammatical environments that require a null pronoun. According to the ''Real Academia Española'', the expression or elision of the subject pronoun is not random. Rather there are contexts in which an overt pronoun is abnormal, while in other cases the overt pronoun is possible or even required. The third person pronouns (''él, ella, ellos'', ''ellas'') in most contexts can only refer to persons. Therefore, when referring to things (that are not people) an explicit pronoun is usually disallowed. Subject pronouns can be made explicit when used for a contrastive function or when the subject is the focus of the sentence. In the following example, the first person explicit pronoun is used to emphasize the subject. :''Yo'' [y no tú u otra persona] ''creo que eso estuvo mal.'' :''I [and not you or another person] think that that was wrong.'' Subject pronouns can also be made explicit in order to clarify ambiguities that arise due to verb forms that are homophonous in the first person and third person. For example, in the past imperfect, conditional, and the subjunctive, the verb forms are the same for first person singular and third person singular. In these situations, using the explicit pronoun ''yo'' (1st person singular) or ''él, ella'' (3rd person singular) clarifies who the subject is, since the verbal morphology is ambiguous.


:''Vedi questo tronco? Andrebbe bene da bruciare. È completamente secco.'' (Italian) :See this log? Would go well for burning. Is completely dry ''(literal, direct translation)'' :Do you see this log? It would be fit for burning. It is completely dry. ''(English gloss)''


Examples of omitted subject: :''Estás a ver este tronco? Seria bom para a fogueira. Secou completamente.'' (European Portuguese) :Are to see this log? Would be good for the campfire. Dried completely ''(literal, direct translation)'' :(Do) you see this log? It would be good for the campfire. It has completely dried. ''(English gloss)'' :''Está vendo esse tronco? Seria bom pra fogueira. Secou completamente.'' (Brazilian Portuguese) :Are seeing this log? Would be good for-the campfire. Dried completely ''(literal, direct translation)'' :(Do) you see this log? It would be good for the campfire. It has completely dried. ''(English gloss)'' Omission of object pronouns is likewise possible when the referent is clear, especially in colloquial or informal language: :''Acho que ele vai rejeitar a proposta, mas pode aceitar.'' :Think that he goes (to-)reject the proposal, but may accept. ''(literally)'' :I think he is going to turn down the proposal, but he may accept it. :''Ainda tem macarrão? Não, papai comeu.'' :Still is there pasta? No, daddy ate. ''(literally)'' :Is there pasta left? No, daddy ate it. The use of the object pronoun in these examples (''aceitá-la'', ''comeu-o'') is the default everywhere but Brazil. :''Ela me procurou ontem e não achou.'' :She me sought yesterday and not found. ''(literally)'' :She looked for me yesterday and didn't find me. Here ''não me achou'' would also be possible. :A: ''Eu te amo; você também me ama?'' B: ''Amo, sim''. :A: I you love; you too me love? B: Love-1-SING, yes. ''(literally)'' :A: I love you; do you love me too? B: I do. Omission of the object pronoun is possible even when its referent has not been explicitly mentioned, so long as it can be inferred. The next example might be heard at a store; the referent (a dress) is clear to the interlocutor. In both Brazilian and European Portuguese the pronoun is omitted. :Viu que bonito? Não gosta? Pode comprar? (BP) ::Saw how beautiful? Don't like? Can buy? (using polite 2nd person) (BP) :Viste que bonito? Não gostas? Podes comprar? (EP) ::Saw how beautiful? Don't like? Can buy? (using informal 2nd person) (EP) :Have you seen how beautiful it is? Do you like it? Can you buy it? ''(English gloss)'' ''Modern'' Spanish and Portuguese are also notable amongst Romance languages because they have no specific pronouns for circumstantial Complement (linguistics), complements (arguments denoting circumstance, consequence, place or manner, modifying the verb but not directly involved in the action) or partitives (words or phrases denoting a quantity of something). However, Medieval language had them, e.g. Portuguese ''hi'' and ''ende''. Compare the following examples in which Spanish, Portuguese, Galician, and Romanian have null pronouns for place and partitives, but Catalan, French, Occitan, and Italian have overt pronouns for place and partitive. Image:EuropeProDropLanguages.png, 300px, Languages in Europe Circumstantial complement denoting place * "I'm going [there]!" ** Spanish language, Spanish ''¡Voy!'' ** Portuguese language, Portuguese ''Vou!'' ** Galician language, Galician ''Vou!'' ** Romanian language, Romanian ''Mă duc!'' ** Catalan language, Catalan ''Hi vaig!'' ** French language, French ''J'y vais !'' ** Occitan language, Occitan ''I vau!'' ** Italian language, Italian ''Ci vado!'' Partitive denoting quantity * "I have four of them." ** Spanish language, Spanish ''Tengo cuatro.'' ** Portuguese language, Portuguese ''Tenho quatro.'' ** Galician language, Galician ''Teño catro.'' ** Romanian language, Romanian ''Am patru.'' ** Catalan language, Catalan ''En tinc quatre.'' ** French language, French ''J'en ai quatre.'' ** Occitan language, Occitan ''N'ai quatre.'' ** Italian language, Italian ''Ne ho quattro.''

Slavic languages

Slavic languages The Slavic languages, also known as the Slavonic languages, are Indo-European languages The Indo-European languages are a language family native to western and southern Eurasia. It comprises most of the languages of Europe together with t ...
behave in a similar manner to the Romance pro-drop languages. Example: :''Бачу [яго]. Ідзе.'' Belarusian language, Belarusian :''Виждам го. Идва.'' Bulgarian language, Bulgarian :''Vidim ga. Dolazi.'' Croatian language, Croatian :''Vidím ho. Jde.'' Czech language, Czech :''Го гледам. Доаѓа.'' Macedonian language, Macedonian :''Widzę go. Idzie.'' Polish language, Polish :''Вижу [его]. Идёт.'' Russian language, Russian :''Видим га. Долази.'' Serbian language, Serbian :''Vidím ho. Ide.'' Slovak language, Slovak :''Vidim ga. Prihaja.'' Slovene language, Slovene :''Бачу [його]. Іде.'' Ukrainian language, Ukrainian :"I see him. He is coming." Here ''he'' in the second sentence is inferred from context. In the East Slavic languages even the objective pronoun "его" can be omitted in the present and future tenses (both imperfect and perfective). As with the Romance languages mentioned above, the missing pronoun is not inferred strictly from pragmatics, but partially indicated by the morphology of the verb (Вижу, Виждам, Widzę, Vidim, etc...). However, the past tense of both imperfective and perfective in modern East Slavic languages inflects by gender and number rather than the person due to the fact that the present tense conjugations of the copula "to be" (Russian ''быть'', Ukrainian ''бути'', Belorussian ''быць'') have practically fallen out of use. As such, the pronoun is often included in these tenses, especially in writing.

Finno-Ugric languages

In Finnish language, Finnish, the verb inflection replaces first and second person pronouns in simple sentences, e.g. ''menen'' "I go", ''menette'' "all of you go". Pronouns are typically left in place only when they need to be inflected, e.g. ''me'' "we", ''meiltä'' "from us". There are possessive pronouns, but possessive suffixes, e.g. ''-ni'' as in ''kissani'' "my cat", are also used, as in ''Kissani söi kalan'' ("my cat ate a fish"). A peculiarity of colloquial Finnish is that the pronoun ''me'' ("we") can be dropped if the verb is placed in the passive voice (e.g. ''haetaan'', standard "it is fetched", colloquial "we fetch"). In the Estonian language, a close relative of Finnish, the tendency is less clear. It generally uses explicit personal pronouns in the literary language, but these are often omitted in colloquial Estonian. Hungarian language, Hungarian is also pro-drop, subject pronouns are used only for emphasis, as example ''(Én) mentem'' "I went", and because of the definite conjugation, object pronouns can be often elided as well; for example, the question ''(Te) láttad a macskát?'' "Did (you) see the cat?" can be answered with just ''láttam'' "(I) saw (it)", because the definite conjugation renders the object pronoun superfluous.


Modern Hebrew, like Biblical Hebrew, is a "moderately" pro-drop language. In general, subject pronouns must be included in the present tense. Since Hebrew has no verb forms expressing the present tense, the present tense is formed using the present participle (somewhat like English ''I am guarding''). The participle in Hebrew, as is the case with other adjectives, declines only in grammatical gender and number (like the ''past'' tense in Russian), thus: :I (m.) guard (''ani shomer'') = :You (m.) guard (''ata shomer'') = :He guards (''hu shomer'') = :I (f.) guard (''ani shomeret'') = :We (m.) guard (''anachnu shomrim'') = Since the forms used for the present tense lack the distinction between grammatical persons, explicit pronouns must be added in the majority of cases. In contrast, the past tense and the future tense the verb form is inflected for person, number, and gender. Therefore, the verb form itself indicates sufficient information about the subject. The subject pronoun is therefore normally dropped, except in third-person. : I (m./f.) guarded (''shamarti'') = :You (m. pl.) guarded (''sh'martem'') = :I (m./f.) will guard (''eshmor'') = :You (pl./m.) will guard (''tishm'ru'') = Many nouns can take suffixes to reflect the possessor, in which case the personal pronoun is dropped. In daily modern Hebrew usage, inflection of nouns is common only for simple nouns, and in most cases, inflected possessive pronouns are used. In Hebrew, possessive pronouns are treated mostly like adjectives and follow the nouns which they modify. In biblical Hebrew, inflection of more sophisticated nouns is more common than in modern usage.

Generalizations across languages

Spanish, Italian, Catalan, Occitan and Romanian can elision, elide subject pronouns only (Portuguese sometimes elides object pronouns as well), and they often do so even when the referent has not been mentioned. This is helped by person/number inflection on the verb. It has been observed that pro-drop languages are those with either rich inflection for person and number (Persian, Polish, Portuguese, etc.) or no such inflection at all (Japanese, Chinese, Korean, etc.), but languages that are intermediate (English, French, etc.) are non-pro-drop. While the mechanism by which overt pronouns are more "useful" in English than in Japanese is obscure, and there are exceptions to this observation, it still seems to have considerable descriptive validity. As Huang puts it, "Pro-drop is licensed to occur either where a language has full agreement, or where a language has no agreement, but not where a language has impoverished partial agreement."Huang, C.-T. James. "On the distribution and reference of empty pronouns". ''Linguistic Inquiry'' 15: 531-574. 1984.

Other language families and linguistic regions

Among the Indo-European and Dravidian languages of India, pro-drop is the general rule though many Dravidian languages do not have overt verbal markers to indicate pronominal subjects. Mongolic languages are similar in this respect to Dravidian languages, and all Paleosiberian languages are rigidly pro-drop. Outside of northern Europe, most Niger–Congo languages, Khoisan languages of Southern Africa and Austronesian languages of the Western Pacific, pro-drop is the usual pattern in almost all linguistic area, linguistic regions of the world. In many non-pro-drop Niger–Congo or Austronesian languages, like Igbo language, Igbo, Samoan language, Samoan and Fijian language, Fijian, however, subject pronouns do not occur in the same position as a nominal subject and are obligatory, even when the latter is present. In more easterly Austronesian languages, like Rapa Nui language, Rapa Nui and Hawaiian language, Hawaiian, subject pronouns are often omitted even though no other subject morphemes exist. Pama–Nyungan languages of Australia also typically omit subject pronouns even when there is no explicit expression of the subject. Many Pama–Nyungan languages, however, have clitics, which often attach to nonverbal hosts to express subjects. The other languages of Northwestern Australia are all pro-drop, for all classes of pronoun. Also, Papuan languages of New Guinea and Nilo-Saharan languages of East Africa are pro-drop. Among the indigenous languages of the Americas, pro-drop is almost universal, as would be expected from the generally polysynthetic language, polysynthetic and head-marking language, head-marking character of the languages. That generally allows eliding of all object pronouns as well as subject ones. Indeed, most reports on Native American languages show that even the emphatic use of pronouns is exceptionally rare. Only a few Native American languages, mostly language isolates (Haida language, Haida, Trumai language, Trumai, Wappo language, Wappo) and the Oto-Manguean languages, Oto-Manguean family are known for normally using subject pronouns.

Pragmatic inference

Classical Chinese exhibits extensive dropping not only of pronouns but also of any terms (subjects, verbs, objects, etc.) pragmatically inferable, giving a very compact character to the language. Note, however, that Classical Chinese was a written language, and such word dropping is not necessarily representative of the spoken language or even of the same linguistic phenomenon.

See also

* *{{annotated link, Zero copula; many languages such as Arabic and Hebrew lack a "to be" verb which is implicit in the subject.


Further reading

*Bresnan, Joan (ed.) (1982) The Mental Representation of Grammatical Relations, MIT Press, Cambridge, Massachusetts. *Chomsky, Noam (1981) Lectures on Government and Binding: The Pisa Lectures. Holland: Foris Publications. Reprint. 7th Edition. Berlin and New York: Mouton de Gruyter, 1993. *Graffi, Giorgio (2001) 200 Years of Syntax. A critical survey, John Benjamins, Amsterdam, The Netherlands. *Moro, Andrea (1997) The raising of predicates. Predicative noun phrases and the theory of clause structure, Cambridge Studies in Linguistics, Cambridge University Press, Cambridge, England. *Rizzi, Luigi (1982) Issues in Italian Syntax, Foris, Dordrecht. *Krivochen, Diego and Peter Kosta (2013) Eliminating Empty Categories. Frankfurt am Main: Peter Lang. *Jaeggli, Osvaldo, and Ken Safir (1989) The Null Subject Parameter. Dordrecht: Kluwer.

External links

List of languages
including pro-drop (PD) or non-pro-drop (NPD) status. Linguistic typology