The conventions that govern acting in general are related to structured forms of play, which involve, in each specific experience, "rules of the game." This aspect was first explored by Johan Huizinga (in "Homo Ludens", 1938) and Roger Caillois (in "Man, Play and Games", 1958). Caillois, for example, distinguishes four aspects of play relevant to acting: "mimesis" (simulation), "agon" (conflict or competition), "alea" (chance), and "illinx" (vertigo, or "vertiginous psychological situations" involving the spectator's identification or catharsis). This connection with play as an activity was first proposed by Aristotle in his "Poetics", in which he defines the desire to imitate in play as an essential part of being human and our first means of learning as children: