Charles Hockett proposed a set of
design features of human language that he thought might be used to compare interspecific communication on more objective grounds. This was in the 1950s, before much laboratory experiment on bird and primate speech has been conducted yet. For Hockett, it was not an either/or question. Some forms of animal communication mirror ours more closely, some are very different. His categories are worth considering at any rate:
Vocal-auditory channel: We favor the voice and our ears to carry the majority of semantic information. (excepting sign languages)
Broadcast transmission and directional reception: Speech is to a room, but we listen to individuals.
Transitoriness We rely on very temporary and passing means of communication, like speech or hand signs, that cease to exist the second they stop broadcasting.
Interchangeability Anyone can produce any valid comunication, in a human language (as opposed to, for instance, animals that produce wholly different sounds or pheremones by sex or role).
Total feedback We can hear ourselves and reflect on the speech we've produced.
Specialization We produce speech intentionally, not as a side product of other biological functions.
Semanticity Speech sounds have specific (albeit flexible) meanings.
Arbitrariness The actual sounds (phonemes) of speech are arbitrary, seldom tied intrinsically to their subject.
Discreteness We use a discrete set of sounds to produce consistent morphophonemic rules, like using the suffix -ed to mark a verb as past tense in English.
Displacement We can talk about things that aren't physically present, which might range from objects in another room to the very gods in the heavens.
Productivity We make up completely new words phrases, and a novel construction doesn't necessarily prevent a listener from understanding what you mean.
Traditional transmission Languages are learned from other humans.
Duality of patterning Human languages have a hierarchical structure of meaning (sentence, morpheme, phoneme) , and each tier operates on a somewhat similar logic of recombinant meaning.
Prevarication We can lie, and indeed do so very frequently.
Reflexiveness We can talk about and think about ourselves, in particular, about language itself.
Learnability Although there are thousands of languagers, fluency in any human language can eventually be acquired through study or experience.