Linguistic Structural Recursion

Human languages both signed and spoken exhibit recursion, here defined as the ability to embed structures of one type within structures of the same type, such as noun phrases within noun phrases (surveys of the number of speakers of the various languages of the world), clauses within clauses (the journalist reported that Chomsky said that Skinner had claimed that language consists solely of observable behavior), or combinations of the two (this is the dog that chased the cat that killed the rat that ate the malt that lay in the house that Jack built). However, there have been claims that Pirahã, a language spoken by a relatively isolated tribe in the Amazon, does not exhibit such structures. Language-trained apes do not appear to produce  recursive structures though there is some evidence that they may comprehend them. There is no evidence for recursive structure in naturally occurring animal communication, though starlings have been trained in the laboratory to recognize a particular type of recursive structure (AⁿBⁿ, not prevalent in human language).