I present two views on what is unique to human language. Hauser, Chomsky & Fitch (2002) hypothesize that the crucial property is a recursive system which links the Sensory-Motor system and the Conceptual-Intentional system. I assume that the distinctive property is that human language has signs: whereas an animal call is an immediate reflex response to a perceptual stimulation, a sign has a nonimmediate and potentially unlimited <i>signifié</i>. This expressive power comes from the arbitrariness of the sign, which has its source in the nature of the two substances involved: as Saussure compellingly argued, there is nothing in the nature of the perceptual substance or the conceptual substance to have any particular pairing. Recursion is a by-product of some of these substantive properties. This model has the advantage that it derives several other novel traits of language which appear to be unconnected in the HCF model. My model also leads to more explanatory analyses of basic syntactic constructions, as illustrated by five key constructions.