Establishing and accounting for the resilient properties of language

Two issues feature in this set of commentaries—issues about establishing the resilient properties of a language, and issues about accounting for them. Homesigners (deaf individuals who generate gesture systems without usable input from a conventional language model) are crucial not only in establishing the existence of resilient properties of a language, but also in setting some constraints on the types of explanations that will work to account for them; the most obvious is that input from a conventional language is not essential for these properties to arise in human communication. But there are other constraints. For example, homesigners produce gestures that are structured along linguistic lines, but they receive in return the co-speech gestures that their hearing family members produce; these gestures are structured around speech, which makes the structure inaccessible to the homesigner. The resilient properties of a language can thus arise in a system that is at the same time produced for others but not received from others. The give-and-take aspect of communication may be less important to the structure of a language than previously thought (cf. Tomasello, 2009). Everett (2015) is, however, not convinced that there is anything to explain. For example, he believes that the homesign studies do nothing more than show that children readily adopt symbols and use these symbols to represent objects because they, unlike other animals, have a strong need to communicate. I do not deny that humans have a strong need to communicate, but what impresses me about homesign is that it is structured communication. There are several points worth making about the structure found in homesign. First, the structures found in homesign resemble structures found in natural language. They did not have to – there are other ways of structuring information. But they do, presumably because they are fashioned by people. Second, the structures found in homesign are often not needed for a communication partner to understand the gestures. For example, homesigners tend to produce a gesture for the object of an action before the gesture for the action verb (an Object-Verb (OV) order, e.g. water–drink, as opposed to drink–water). It is obvious from shared context (cf. Forrester & Thomas, 2015) that the water is the object of drink, not the other way around. Nonetheless, homesigners all use OV order in their gesture sentences. (As an aside in response to Everett, the OV order cannot be reduced to new and old categories of information, see Goldin-Meadow & Mylander, 1984, 50–51.) Everett asserts that it is easier to select one order and run with it, rather than waffle between two orders. But there are no data to back up this assertion. Third, the structures found in homesign are not found in the natural gestures that non-human primates use to communicate (Cartmill, Beilock, & Goldin-Meadow, 2012), nor are they found in the gestures, signs, or symbols nonhuman primates produce when taught a communication system. Relevant to the preceding point, even when taught a sign language, a chimpanzee does not use consistent order to convey relational information (Terrace, Petitto, Sanders, & Bever, 1979). It does not appear to be easier for a chimp to follow a single order than to produce random orders – at the least, this is a bias that is unique to humans. Fourth, the structures found in homesign are not found in the gestures that speakers spontaneously produce when they talk. Again, in terms of order, an individual’s cospeech gestures do not follow a consistent order, even though the gestures they produce when they are asked not to talk (their silent gestures) do (Goldin-Meadow, McNeill, & Singleton, 1996). In terms of accounting for the resilient properties of language, as Forrester and Thomas (2015) point out, these properties need not be traceable to innate structures, although here it is important to be clear about what we mean by innate. Innateness has been addressed repeatedly and elegantly in many disciplines, particularly ethology (e.g. Lehrman, 1970; Mayr, 1974; McClintock, 1980), and as many as 17 definitions of innateness have been proposed (Wimsatt, 1986). The most common definition assumes that the development of innate behaviours is guided by a genetic programme. But we can also think about the development of innate behaviours as being