||This article needs additional citations for verification. (November 2012)|
Typically, null-subject languages express person, number, and/or gender agreement with the referent on the verb, rendering a subject noun phrase redundant. In the principles and parameters framework, the null subject is controlled by the pro-drop parameter, which is either on or off for a particular language.
For example, in Italian the subject "she" can be either explicit or implicit:
- Maria non vuole mangiare. lit. Maria not want [to]-eat, "Maria does not want to eat".
- Non vuole mangiare. lit. Subject not want [to]-eat, "[(S)he] does not want to eat."
Of the thousands of languages in the world, a considerable part are null-subject languages, from a wide diversity of unrelated language families. They include Albanian, Hebrew, Arabic, Basque, Finnish, Hindi, Hungarian, Italian, Romanian, Catalan, Chinese, Japanese, Korean, Persian, European Portuguese, Polish and other Slavic languages, Spanish, Greek, Tamil and Turkish, as well as most languages related to these, and many others still. In fact it is rather non-pro-drop that is an areal feature of Standard Average European including French, German, and English.
In the framework of government and binding theory of syntax, the term null subject refers to an empty category. The empty category in question is thought to behave like an ordinary pronoun with respect to anaphoric reference and other grammatical behavior. Hence it is most commonly referred to as "pro".
This phenomenon is similar, but not identical, to that of pro-drop languages, which may omit pronouns, including subject pronouns, but also object pronouns. While pro-drop languages are null-subject languages, not all null-subject languages are pro-drop.
In null-subject languages that have verb inflection in which the verb inflects for person, the grammatical person of the subject is reflected by the inflection of the verb, and likewise for number and gender.
The following examples come from Portuguese:
- "I'm going home" can be translated either as Vou para casa or as Eu vou para casa, where eu means "I".
- "It's raining" can be translated as Está chovendo, but not as *Ele está chovendo, where ele would correspond to English it.
- "I'm going home. I'm going to watch TV" would not, except in exceptional circumstances, be translated as Eu vou para casa. Eu vou ver televisão. At least the subject of the second sentence should be omitted in Portuguese unless one wishes to express emphasis, as to emphasise the I.
As the examples illustrate, in many null-subject languages, personal pronouns exist and can be used for emphasis but are dropped whenever they can be inferred from the context. Some sentences do not allow a subject in any form while, in other cases an explicit subject without particular emphasis, would sound awkward or unnatural.
Latin language 
Latin text: Veni, vidi, vici.
Literal translation: came, saw, conquered.
Idiomatic translation: I came, I saw, I conquered.
Latin text: Cogito ergo sum.
Literal translation: think, therefore am.
Idiomatic translation: I think, therefore I am.
Tamil language 
Tamil script: முடிந்துவிட்டது
Literal Translation: ended
Actual Translation: It has come to an end.
Hebrew language 
Hebrew is considered a partially null-subject language, as demonstrated by the following example:
Hebrew text: עזור לאחרים, יעזרו לך
Transliteration: azor l'aherim, ya'azru lkha
Literal translation: help others, they-will-help you
Idiomatic translation: you help others, they will help you.
Subjects can usually omitted only when there is rich person cross-marking on the verb, as in third person plural in the example above.
Arabic language 
Arabic is considered a null-subject language, as demonstrated by the following example:
Arabic text: ساعد غيرك، يساعدك
Transliteration: sā‘id ghayrak, yusā‘iduk
Literal translation: help other, helps you
Idiomatic translation: You help another, he helps you.
Japanese language 
Japanese and several other null-subject languages are topic-prominent languages; some of these languages require an expressed topic in order for sentences to make sense. In Japanese, for example, it is possible to start a sentence with a topic marked by the particle wa, and in subsequent sentences leave the topic unstated, as it is understood to remain the same, until another one is either explicitly or implicitly introduced. For example, in the second sentence below, the subject ("we") is not expressed again but left implicit:
|Transliteration||Watashitachi wa||kaimono o||shita.||Ato de||gohan o||tabeta.|
|Literal translation||We (TOPIC)||shopping (OBJ)||did.||After (COMPL)||dinner (OBJ)||ate.|
|Idiomatic translation||"We went shopping. Afterwards, we ate dinner."|
In other cases, the topic can be changed without being explicitly stated, as in the following example, where the topic changes implicitly from "today" to "I".
|Transliteration||Kyō wa||gēmu no||hatsubaibi||na n da||kedo,||kaō ka||dō ka||mayotte iru.|
|Literal translation||Today (TOPIC)||game (GEN)||release date||is||but,||whether to buy||or not||confused.|
|Idiomatic translation||"The game comes out today, but (I) can't decide whether or not to buy (it)."|
Spanish language 
In Spanish, the subject is encoded in the verb conjugation. Pronoun use is not obligatory.
- (Nosotros) Vamos a la playa: We go to the beach.
- (Tú/vos) Eres/sos mi amiga: You are my friend.
- (Ustedes/vosotros) No son/sois bienvenidos aquí: You are not welcome here.
- (Ellos) Están durmiendo: They are asleep.
- (Yo) Necesito ayuda: I need help.
- (Él) Está en su habitación: He is in his bedroom.
- (Ella) Está cansada: She is tired.
In Spanish, one may choose whether to use the subject or not. If used in an inclined tone, it may be seen as an added emphasis; however, in colloquial speaking, usage of a pronoun is optional. Even so, sentences with a null subject are used more frequently than sentences with a subject. In some cases, it is even necessary to skip the subject to create a grammatically correct sentence.
Macedonian language 
Дојдов, видов, победив ("Veni, vidi, vici").
Literal translation: came, saw, conquered.
Idiomatic translation: I came, I saw, I conquered.
Impersonal constructions 
In some cases (impersonal constructions), a proposition has no referent at all. Pro-drop languages deal naturally with these, whereas many non-pro-drop languages such as English and French have to fill in the syntactic gap by inserting a dummy pronoun. "*Rains" is not a correct sentence; a dummy "it" has to be added: "It rains", French "Il pleut". In most Romance languages, however, "Rains" can be a sentence: Spanish "Llueve", Italian "Piove", Catalan "Plou", Portuguese "Chove", Romanian "Plouǎ", etc. Uralic and Slavic languages also show this trait: Finnish "Sataa", Hungarian "Esik"; Polish "Pada".
There are some languages that are not pro-drop but do not require this syntactic gap to be filled. For example, in Esperanto, "He made the cake" would translate as Li faris la kukon (never *Faris la kukon), but It rained yesterday would be Pluvis hieraŭ (not *Ĝi pluvis hieraŭ).
Null subjects in non-null-subject languages 
Other languages (sometimes called non-null-subject languages) require each sentence to include a subject: this is the case for most Germanic languages, such as English and German, but also in French (unlike most other Romance language), and many others. In some cases, colloquial expressions, particularly in English, less so in German, and occasionally in French, allow for the omission of the subject in the same way that languages such as Spanish and Russian allow using "correct" grammar:
- "Bumped into George this morning." (I)
- "Agreed to have a snifter to catch up on old times." (We)
- "Told me what the two of you had been up to." (He)
- "Went down to Brighton for the weekend?" (You)
The imperative form 
Even in such non-null-subject languages as English, it is standard for clauses in the imperative mood to lack explicit subjects; for example:
- "Take a break; you're working too hard."
- "Shut up!"
An explicit declaration of the pronoun in English in the imperative mood is possible, usually for emphasis but not necessary:
- "Don't you listen to him!"
French and German offer less flexibility with regards to null subjects. In French, it is neither grammatically correct nor possible to include the subject within the imperative form (the vous in the expression taisez-vous would stem from the fact that se taire, to be silent is a reflexive verb and is thus the object).
In German, the informal form du may be added to the imperative in a colloquial manner for emphasis (Mach du das, you do it). The formal imperative requires the addition of the subject Sie (as in Machen Sie das) because the formal, addressee-specific imperative form of a verb is morphologically identical to the infinitive, which when used by itself belongs in final position and indicates a "neutral" or addressee-nonspecific imperative (e.g., "Bitte nicht stören" ["Please do not disturb"]).
Pro-drop in infants 
||This section may require cleanup to meet Wikipedia's quality standards. (June 2010)|
Research shows that until around three years old, children often omit subjects. For example:
- Drop bean.
- Brushing my teeth.
- Going to school.
- Want an apple.
Auxiliary languages 
Many international auxiliary languages, while not officially pro-drop, permit pronoun omission with some regularity.
In Interlingua, pronoun omission is most common with the pronoun il, which means "it" when referring to part of a sentence or to nothing in particular. Examples of this word include
- Il pluvia.
- It's raining.
- Il es ver que ille arriva deman.
- It is true that he arrives tomorrow.
Il tends to be omitted whenever the contraction "it's" can be used in English. Thus, il may be omitted from the second sentence above: "Es ver que ille arriva deman". In addition, subject pronouns are sometimes omitted when they can be inferred from a previous sentence:
- Illa audiva un crito. Curreva al porto. Aperiva lo.
- She heard a cry. Ran to the door. Opened it.
Similarly, Esperanto sometimes exhibits pronoun deletion in casual use. This deletion is normally limited to subject pronouns, especially where the pronoun has been used just previously:
- Ĉu vi vidas lin? Venas nun.
- QUESTION-PARTICLE you see him? Comes now.
- Do you see him? He is coming now.
In "official" use, however, Esperanto admits of null-subject sentences in two cases only:
- (optional) in the 2nd person imperative (N.B. The Esperanto imperative is often named "volitive" instead, since it can be conjugated with a subject in any person, and also used in subordinate clauses)
- Venu! Come!
- Vi venu! You [there], come [with me]! (pronoun added for emphasis)
- For "impersonal verbs" which have no semantic subject. In English or French, an "empty" subject is nevertheless required:
- Pluvas. It is raining. FR: Il pleut.
- Estas nun somero. It is summer now. FR: C'est l'été à présent.
- Estas vere, ke li alvenos morgaŭ. It is true that he will arrive tomorrow. FR: C'est vrai qu'il arrivera demain.
- (In this latter case, the sentence is not really no-subject, since "ke li alvenos morgaŭ" ("that he will arrive tomorrow") is the subject.)
Contrary to the Interlingua example above, and as in English, a repeated subject can normally be omitted only within a single sentence:
- Ŝi aŭdis krion. Ŝi kuris al la pordo. Ŝi malfermis ĝin.
- She heard a shout. She ran to the door. She opened it.
- Ŝi aŭdis krion, kuris al la pordo kaj malfermis ĝin.
- She heard a shout, ran to the door and opened it.
- Martin Haspelmath, The European linguistic area: Standard Average European, in Martin Haspelmath, et al., Language Typology and Language Universals, vol. 2, 2001, pp. 1492-1510
- P Barbosa, MEL Duarte, and M Kato. (2005) Null Subjects in European and Brazilian Portuguese. Journal of Portuguese Linguistics. ()
- Cook, Manuela. (1997) A Theory for the Interpretation of Forms of Address in the Portuguese Language. Hispania, Vol 80, Nº 3, AATSP, USA
- Chomsky, N. (1981). Lectures on Government and Binding: The Pisa Lectures. Holland: Foris Publications, Reprint. 7th Edition. Berlin and New York: Mouton de Gruyter, 1993.