Definition
Language, in Harari's usage, is the open-ended symbolic communication system that Sapiens acquired around the time of the Cognitive Revolution. Other animals communicate — vervet monkeys have distinct alarm calls for leopard, eagle, and snake — but their communication is anchored to immediate, observable features of the environment. Sapiens language is not.
The defining capability is reference to the absent. With Sapiens language you can talk about food that is not in front of you, hunts that have not yet happened, ancestors who are dead, gods who never existed, and corporations that exist only because everyone agrees they do. That single capability — flexible reference — is the engine of everything else Harari describes.
Why it matters
How it works
Sapiens language combines a small set of phonemes into an unbounded set of words, and a finite grammar generates an unbounded set of sentences. The same finite resources can describe a leopard sighting, a debt owed, a marriage rite, a battle plan, or a hypothetical god. Whatever the mind can compose, the language can transmit.
This is qualitatively different from a fixed signal system. A vervet monkey's alarm calls are powerful but rigid. Sapiens language is plastic. It can be repurposed to describe anything new — a steam engine, a stock option, a software bug — without needing to evolve a new biology.