In game theory a move by nature is a decision or move in an extensive form game made by a player who has no strategic interests in the outcome. The effect is to add a player, 'Nature' whose practical role is to act as a random number generator. For instance, a game of Poker requires a dealer to choose which cards a player is dealt, the dealer plays the role of the Nature player
Fig.1 shows a signaling game which begins with a move by nature. Moves by nature are an integral part of games of incomplete information.