Joint activities advance mostly through joint actions. In buying items in a drugstore, a customer joins a server in opening the transaction, settling on the items wanted, establishing the price, exchanging money, and closing. In a chess game, the players join in specifying discrete moves from the opening of the game to the checkmate. Joint actions like these belong to an extended family of actions that also includes moving together in waltzing, playing notes together in a string quartet, paddling in unison in a canoe, and passing a ball in soccer or basketball. It also includes asking questions, making requests, making assertions, making references – much of what we think of as language use.

What makes an action a joint one, ultimately, is the coordination of individual actions by two or more people. There is coordination of both content, what the participants intend to do, and processes, the physical and mental systems they recruit in carrying out those intentions. When Ann and Ben paddle a canoe together, they coordinate on their plans – the content of what they do. Overall, they aim to reach the spit of land on the other side of the lake as efficiently as possible, with Ann in front and Ben in the rear. At any moment, they aim to stay on course, with Ann pulling on one side and Ben on the other. Ann and Ben also coordinate on their physical and mental processes.