Social play is naturally characterized in intentional terms. An evolutionary account of social play could help scientists to understand the evolution of cognition and intentionality. Alexander Rosenberg (1990) has argued that if play is characterized intentionally or functionally, it is not a behavioral phenotype suitable for evolutionary explanation. If he is right, his arguments would threaten many projects in cognitive ethology. We argue that Rosenberg's arguments are unsound and that intentionally and functionally characterized phenotypes are a proper domain for ethological (...) investigation. (shrink)