 With chess it is possible , in principle , to play a perfect game or construct a machine to do so as follows : One considers in a given position all possible moves , then all moves for the opponent , etc . , to the end of the game ( in each variation ) . The end must occur , by the rules of the games after a finite number of moves ( remembering the 50 move drawing rule ) . Each of these variations ends in win , loss or draw . By working backward from the end one can determine whether there is a forced win , the position is a draw or is lost . It is easy to show , however , even with the high computing speed available in electronic calculators this computation is impractical . In typical chess positions there will be of the order of 30 legal moves . The number holds fairly constant until the game is nearly finished as shown ... by De <unk> , who averaged the number of legal moves in a large number of master games . Thus a move for White and then one for Black gives about 103 possibilities . A typical game lasts about 40 moves to resignation of one party . This is conservative for our calculation since the machine would calculate out to <unk> , not resignation . However , even at this figure there will be <unk> variations to be calculated from the initial position . A machine operating at the rate of one variation per <unk> would require over <unk> years to calculate the first move ! 
