Primate vocalisations are irrepressible, context-bound indices of emotional states, in some cases conveying additional information about the sender's condition, status and/or local environment. Speech has a quite different function: it permits communication of information concerning a shared, conceptual environment – a world of intangibles independent of currently perceptible reality.

A suite of formal discontinuities are bound up with this fundamental functional contrast. Whereas primate vocalisations are not easily faked, human speech signals are cognitively controlled, linked arbitrarily to their referents and ‘displaced’ – hence immune from contextual corroboration (Burling 1993). The meanings of primate gestures/calls are evaluated on an analog, ‘more/less’ scale; speech signals are digitally processed (Burling 1993). When combined, primate signals and associated meanings blend and grade into one another; the basic elements of speech are discrete/particulate (Abler 1989; Studdert-Kennedy 1998). Primate recipients evaluate details of signalling performance; in speech, the focus is on underlying intentions, with listeners compensating for deficiencies in performance (Grice 1969; Sperber and Wilson 1986).