"Work consists of whatever a body is obliged to do," Mark Twain has written. ". . . Play consists of whatever a body is not obliged to do." This distinction, as Tom Sawyer learns and lives it, is what stands between being ordered to whitewash a fence and allowing other boys for a consideration to whitewash that fence. Comparably, though we might not think of Immanuel Kant as a prime exponent of the pleasure principle, his esthetics were based upon the conception of free play, a purely disinterested mode of activity. That autotelic impetus was expressed more emphatically by his poetic disciple, Friedrich Schiller: "Man plays only when he is in the fullest sense of the word a human being, and he is only a complete human being when he plays." Man is a playful if not an entirely rational animal, by Aristotelian definition the sole animal who laughs. Schiller speaks of Spieltrieb y the play instinct, the urge toward esthetic pleasure, Spiel signifying game and likewise drama in German: Schauspiel (show-game), Trauerspiel (mourning-game or tragedy), Lustspiel (pleasure-game or comedy). We encounter the same double meaning in the English word play, as well as in the French jeu and the Latin ludus. Though there is no parallel in Greek, it is significant that drama was derived from a root which means act, another ambiguity. Play itself primarily connoted movement or exercise, as in swordplay, and has often been connected with music, as in playing an instrument.