Joseph Greenberg in the context of "Amerindian language"

The Indigenous languages of the Americas are the languages that were used by the Indigenous peoples of the Americas before the arrival of Europeans. Over a thousand of these languages are still used today, while many more are now extinct. The Indigenous languages of the Americas are not all related to each other; instead, they are classified into a hundred or so language families and isolates, as well as several extinct languages that are unclassified due to the lack of information on them.

Many proposals have been made to relate some or all of these languages to each other, with varying degrees of success. The most widely reported is Joseph Greenberg's Amerind hypothesis, which, however, nearly all specialists reject because of severe methodological flaws; spurious data; and a failure to distinguish cognation, contact, and coincidence.

The Khoisan languages (/ˈkɔɪsɑːn/ KOY-sahn; also Khoesan or Khoesaan) are a number of African languages once classified together, originally by Joseph Greenberg. Khoisan is defined as those languages that have click consonants and do not belong to other African language families. For much of the 20th century, they were thought to be genealogically related to each other, but this is no longer accepted. They are now held to comprise three distinct language families and two language isolates.

All but two Khoisan languages are indigenous to southern Africa; these are classified into three language families. The Khoe family appears to have migrated to southern Africa not long before the Bantu expansion. Ethnically, their speakers are the Khoekhoe and the San (Bushmen). Two languages of eastern Africa, those of the Sandawe and Hadza, were originally also classified as Khoisan, although their speakers are ethnically neither Khoekhoe nor San.

Amerind is a widely rejected higher-level language family proposed by Joseph Greenberg in 1960 and elaborated by his student Merritt Ruhlen. Greenberg proposed that all of the indigenous languages of the Americas belong to one of three language families, the previously established Eskimo–Aleut and Na–Dene, and with everything else—otherwise classified by specialists as belonging to dozens of independent families—as Amerind. Because of a large number of methodological issues with the 1987 book Language in the Americas, the relationships he proposed between these languages have been rejected by the majority of historical linguists as spurious.

The term Amerind is also occasionally used to refer broadly to the various indigenous languages of the Americas without necessarily implying that they are a genealogical group. To avoid ambiguity, the term Amerindian is often used for the latter meaning.

A linguistic universal is a pattern that occurs systematically across natural languages, potentially true for all of them. For example, All languages have nouns and verbs, or If a language is spoken, it has consonants and vowels. Research in this area of linguistics is closely tied to the study of linguistic typology, and intends to reveal generalizations across languages, likely tied to cognition, perception, or other abilities of the mind. The field originates from discussions influenced by Noam Chomsky's proposal of a universal grammar, but was largely pioneered by the linguist Joseph Greenberg, who derived a set of forty-five basic universals, mostly dealing with syntax, from a study of some thirty languages.

Though there has been significant research into linguistic universals, in more recent time some linguists, including Nicolas Evans and Stephen C. Levinson, have argued against the existence of absolute linguistic universals that are shared across all languages. These linguists cite problems such as ethnocentrism amongst cognitive scientists, and thus linguists, as well as insufficient research into all of the world's languages in discussions related to linguistic universals, instead promoting these similarities as simply strong tendencies.

The Indigenous languages of the Americas are the languages that were used by the Indigenous peoples of the Americas, before the arrival of Europeans. Over a thousand of these languages are still used in the 21st century, while many more are now extinct. The Indigenous languages of the Americas are not all related to each other; instead, they are classified into a hundred or so language families and isolates, as well as several extinct languages that are unclassified due to the lack of information on them.

Many proposals have been made to relate some or all of these languages to each other, with varying degrees of success. The most widely reported is Joseph Greenberg's Amerind hypothesis; however, nearly all specialists reject it because of severe methodological flaws; spurious data; and a failure to distinguish cognation, contact, and coincidence.