  A common refrain in response to such arguments is that, in situations of partial information, “absence of evidence is not evidence of absence”. Descartes dismissed parrots vocalizing human words because he thought it was merely meaningless repetition. This judgment may have been appropriate for the few parrots he encountered, but it was not based on a systematic, scientific investigation of the capacities of parrots. Nowadays many would argue that Pepperberg's study of the African Grey parrot “Alex” (Pepperberg 1999) should lay the Cartesian prejudice to rest. This study, along with several on the acquisition of a degree of communicative competence by chimpanzees and bonobos (e.g., Gardner et al. 1989; Savage-Rumbaugh 1996) would seem to undermine Descartes' assertions about lack of meaningful communication and general reasoning abilities in animals. (See, also, contributions to Hurley &amp; Nudds 2006.)