In everyday speech there are often instances when who or what is being referred to can be inferred from context. Proponents of the term "pro-drop" take the view that pronouns which in other languages would have those referents can be omitted, or be phonologically null. Among major languages, what might be called a pro-drop language is Japanese (featuring pronoun deletion not only for subjects, but for practically all grammatical contexts). Chinese, Slavic languages, and American Sign Language also exhibit frequent pro-drop features.
Some languages might be considered only partially pro-drop in that they allow deletion of the subject pronoun. These null subject languages include many Romance languages such as Spanish, Italian, Occitan, Catalan, Portuguese, and Romanian (French is the most notable exception), as well as all the Balto-Slavic languages.
Consider the following examples from Japanese:
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. If nouns or pronouns were supplied, the resulting sentences would be grammatically correct but unnatural. (Learners of Japanese as a second language, especially those whose first language is non-pro-drop like English or French, often make the mistake of supplying personal pronouns where pragmatically inferable. This is an example of language transfer.)
English is considered a non-pro-drop language. Nonetheless, subject pronouns are almost always dropped in commands (e.g., Come here); and in informal speech, pronouns and other words, especially copulas and auxiliaries, may sometimes be dropped, especially from the beginnings of sentences:
When answering a question, the sentence structure of the question is often dropped from the answer.
In speech, when pronouns are not completely dropped, they are more often elided than other words in an utterance.
Note that these elisions are generally restricted to very informal speech and certain fixed expressions, and the rules for their use are complex and vary among dialects.
Most Romance languages (with the notable exception of French) are often categorised as pro-drop too, although 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 of the verb. Example:
Spanish and Portuguese are also notable amongst Romance languages because they have no specific pronouns for circumstantial 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). Compare the following:
All Slavic languages behave in a similar manner to the Romance pro-drop languages. Example:
Here he in the second sentence is inferred from context. In Russian even the objective pronoun "его" can be omitted in the present and future tenses (both imperfect and perfective). In most Slavic languages (especially the East Slavic ones), this rule is broken in the past tense of both imperfective and perfectve, since the conjugations agrees with the gender of the person. 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, Widzę, Vidim, etc...)
In 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". In the Estonian language, a close relative of Finnish, the tendency is less clear. It generally uses explicit personal pronouns in written language, but these are often omitted in spoken language.
Hungarian is also pro-drop, subject pronouns are used only for emphasis, as example (Én) megyek "I go", 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 are not dropped in the present tense, because a Hebrew verb in the present tense contains information about the subject. The following examples are illustrative :
Since the verb form itself does not distinguish between the first and third person, the pronouns in this case are not normally dropped.
In contrast, the past tense and the future tense are composed of "non-degenerate" conjugations — the verb has a different form for each grammatical person, and a properly conjugated verb contains all the information about the subject. The subjective pronoun is therefore normally dropped.
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, personal pronouns are used. In Hebrew, personal 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.
Outside of northern Europe, most non-Bantu 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 regions of the world. In many non-pro-drop Niger-Congo or Austronesian languages like Igbo, Samoan or Fijian, however, the 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 Rapanui and 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 non-Pama-Nyungan languages of Northwestern Australia are universally pro-drop for all classes of pronoun. Papuan languages of New Guinea and Nilo-Saharan languages of East Africa are similarly universally pro-drop.
Among Native American languages, pro-drop is almost universal, as would be expected from the generally polysynthetic and head-marking character of the languages. This character generally allows eliding of all object pronouns as well as subject ones: indeed, most reports on Native American languages show even emphatic use of pronouns exceptionally rare. Only a few Native American languages, mostly language isolates (Haida, Trumai) are known to normally use subject pronouns.