WHAT ARE CONVENTIONAL SIGNALS

Confusion over the validity of 'conventional signalling' may have resulted at least in part because it has been used to refer to different concepts. The main aim of this paper is to expose the source of this confusion, not to prescribe a particular solution. Two key current senses of conventional signals are identified: (1) as strategic correlates of quality (or, more generally, of the parameter about which information is contained in the signal's message); (2) as signals whose design is arbitrarily related to their message. The sometimes difficult relationships between these two senses and other concepts in the signalling literature (assessment signals, strategic choice handicaps, direct indicators, revealing handicaps) are explored. It is concluded that two separate but important distinctions have been used to characterize conventional signals (first, whether or not signals allow strategic choice, and, second, whether signalling costs are intrinsic to the signal's production), and that these remain of significance to the understanding of signal design. The paper concentrates mainly on signalling between parties with conflicting evolutionary interests, but briefly shows how these concepts may relate to signalling systems with no conflict of interest.