Bekoff, M. and Allen, C. (1992) Intentional icons: Towards an evolutionary cognitive ethology. Ethology 91:1--16

In most species in which social play has been observed, play-soliciting signals have evolved. These social signals appear to be important in communicating play intention. Here, using the work of RUTH MILLIKAN as a working guide and canid play bows as an example, we argue that (i) some play signals may be simple "intentional icons" and (ii) senders and receivers are "cooperating devices," in that the disposition of senders to produce play-soliciting signals and the disposition of receivers of play signals to respond appropriately to play invitations, have evolved together. MILLIKAN'S views of social communication are difficult to render and are virtually untested. However, her stance, while philosophically controversial, is somewhat consistent with early ethological views of social communication. Thus, in combination with classical ethological positions, MILLIKAN'S position could serve as a useful guide not only to inform and motivate future empirical research in cognitive ethology, but also to stimulate ethologists to reconsider, in innovative ways, nonhuman animal cognition. To reject the empirical utility of MILLIKAN'S theory because of its difficulty or on philosophical grounds would be premature and would represent a confusion of empirical with philosophical issues.