Now let us distinguish three possible varieties of machines: the first and most interesting desires to play and secondarily to win, need not be told the rules of the game, if only his opponent will not play unless the machine abides by the rules. He can derive them by induction, with exactly the same circuits and memory that he used to improve his play when he already knew the rules of the game; the second has the rules of the game programmed into them in advance; the third has their components so connected that they can play only according to the rules. I shall call the first ethical machines. They are free in the sense that we, their creators, have neither told them what they ought to do, nor so made them that they cannot behave inappropriately. The second machine is like a man who enjoys a religion revealed to him personally or through tradition. I shall call him a moral machine. He would have been free, had he not been programmed with the rules of conduct. The third machine is likewise not free. He is at best naturally virtuous, like the Noble Savage. These machines do not differ fundamentally otherwise. They may be equally clever at playing, and their games equally good, or equally likely to win. Now the ethical machine has the great advantage over the other machines in that he can learn to play [any] game he finds the accepted mode of behavior in his society. He will, of course, have difficulties which the moral and virtuous machines will never encounter. He can never know the rules of the game more than tentatively; for the stochastic horses of Opinion drag no chariot to absolute certainty. He must be content to round off his numerical calculations when he has achieved some degree of probability and act on them. If his antagonist cheats in any consistent way, he will include this sort of cheating in what he takes to be the rules. It is probably part of the price we pay for the realism. This uncertainty of the rules for the ethical machine puts him at a disadvantage to the moral and virtuous.