Pro-drop language (from "pronoun-dropping") is a language where pronouns can be elided (deleted) when considered unnecessary or redundant by the speaker.

In everyday speech there are often instances when it is obvious who or what is being referred to, or it can be guessed from context. In a pro-drop language, the pronouns that would normally take the place of those referents can be elided once the context has been established. Among major languages, the prototype of pro-drop languages is probably Japanese (featuring pronoun elision not only for subjects, as is often implied, but for practically all grammatical contexts), but Romance languages such as Portuguese, Spanish, Italian and Romanian are also pro-drop.

Examples

Consider the following examples from Japanese:

Kono kēki wa oishii. Dare ga tsukutta no?

this cake TOPIC tasty. who SUBJECT make-PAST?

"This cake is tasty. Who made it?"

Shiranai. Ki ni itta?

know-NEGATIVE. like-PAST?

"I don't know. Do you like it?"

The pronouns 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. They could be mentioned and the sentences would be grammatically correct, but not natural (learners of Japanese as a second language, especially those whose first language is non-pro-drop like English, often make the mistake of repeating the personal pronouns where they should be dropped).

English deletes subject pronouns in some restricted contexts (Got it?, Makes sense., Feels OK to me., Found it.), but those can be interpreted as informal shortcuts rather than fully grammatical propositions.

Portuguese, Spanish, Italian and Romanian can elide subject pronouns only, and they often do even when the referent has not been mentioned, but this is helped by the fact that verbs in these three languages have a person/number inflection.

In Finno-Ugric languages such as 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 no possessive pronouns, but possessive suffixes, e.g. -ni as in kissani "my cat".

Impersonal constructions

In some cases (impersonal constructions), a proposition has no referent at all. Pro-drop languages deal naturally with these, where non-pro-drop languages such as English and French sometimes have to fill in the syntactic gap by inserting a dummy pronoun. For example, just "Rains" is not a correct sentence, but a dummy "it" has to be added: It rains.