 Secondly, the production of outcome F by system S is supposed to have been stabilized by a process of natural selection, a process of individual learning, or by having contributed to the survival of S. In other words, F must be an etiological function of S, although it should be noted that Shea expands the processes that can ground such functions by including past contributions to survival in addition to natural selection and learning. (Furthermore, Shea allows that representational systems may have design functions instead of stabilized functions, so stabilization is not strictly necessary for representation; cf. Shea 2018, 64–65.)