It has become a truism that paizō means “to behave like a child” or perform “the spirit of childhood”, but what exactly does this mean? This chapter explores this childish mode of being as perceived by various authors, such as Diogenes of Apollonia, Plato, Aristotle, Chrysippus, and anonymous medical writers. From Homer onward, children are described as intellectually inferior to adults, and at least from the time of Heraclitus this intellectual inferiority is related to the decreased cognitive capabilities that adults experience during intoxication. But this cognitive incapacity has a positive flipside: for both children and intoxicated adults there is a physiological state of heightened pleasure. As Aristotle says, the young share the condition of the intoxicated as part of “their nature”. Deferral of pleasure for the sake of some longer-term goal—the act of reason par excellence—becomes impossible, and all that is functionally left for both groups is enjoyment and the acting out of that enjoyment. This heightened state of pleasure—one which motivates certain actions, but is not necessarily caused by those actions—offers the central clue about play’s physiological origins; after all, the verb that regularly charactizes the activities of both children and intoxicated adults is “play” (paizō).