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Can chimpanzees learn sign language or use symbols?

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A common chimpanzee (Pan troglodytes) sits on a rock holding a long blade of grass in its mouth, with dense green foliage in the background. — chimpanzee The West African, or masked, chimpanzee (*Pan troglodytes verus*) is a critically endangered subspecies of chimpanzee.

Researchers have successfully taught chimpanzees to communicate using sign language and systems based on pictorial symbols or tokens. Because the vocal tract of an ape differs significantly from that of a human, early attempts to teach chimpanzees to speak were unsuccessful; however, nonvocal methods have yielded impressive results.123

Notable examples include:
* Washoe: A chimpanzee who learned over 150 signs in American Sign Language to express requests, identify objects, and communicate with trainers.23
* Sarah: A chimpanzee trained to use plastic tokens as words, demonstrating an ability to categorize items and understand basic relationships between symbols.2
* Kanzi: A pygmy chimpanzee (bonobo) who learned to communicate using keyboard symbols and demonstrated an understanding of spoken English.2

While these studies show that chimpanzees can acquire vocabularies and use signs to make requests, the extent to which they understand these as abstract "words" or possess true syntactic language remains a subject of intense debate among scientists. Critics argue that some behaviors may be imitative or prompted by trainers, rather than evidence of spontaneous, complex linguistic ability.12