While we tend to think of communication as the primary function of human language, it is not a distinguishing feature. All creatures communicate in some way. However, we suspect that other creatures are not reflecting on the way they create their communicative messages or reviewing how they work (or not). That is, one barking dog is probably not offering advice to another barking dog along the lines of “Hey, you should lower your bark to make it sound more menacing.” They’re not barking about barking. Humans are clearly able to reflect on language and its uses (e.g. “I wish he wouldn’t use so many technical terms”). This is reflexivity. The property of reflexivity (or “reflexiveness”) accounts for the fact that we can use language to think and talk about language itself, making it one of the distinguishing features of human language. Indeed, without this general ability, we wouldn’t be able to reflect on or identify any of the other distinct properties of human language. We’ll look in detail at another five of them: displacement, arbitrariness, productivity, cultural transmission and duality.