**First, what is language, and how does it differ from other forms of communication? There does not exist a universally accepted definition of language, or criteria for its use; this is one of the reasons for the disagreement among scientists about whether apes can use language. Language consists of various aspects which people believe are more or less important, for example, grammar, symbol usage, the ability to represent real-world situations, and the ability to articulate something new (Wallman 1992: 6). Duane Rumbaugh describes language as "an infinitely open system of communication" (Rumbaugh 1977b: xx). Some people say that anything an ape can do is not language; of course, if these are the same people who say that language defines us as humans, and an ape can learn sign language, then they are saying that deaf people who use sign language are not human (Patterson & Linden 1981: 119-120). One famous view of language is Charles Hockett's seven key properties: duality, productivity, arbitrariness, interchangeability, specialization, displacement, and cultural transmission (Linden 1974: 137). I will return to these properties later in the essay…