Excerpt from Cognitive Wheels

by Daniel Dennett

Reference: Dennet, D. Cognitive Wheels: The Frame Problem in AI. In Minds, Machines, and Evolution. C. Hookway, ed. Pp. 128-151. Cambridge University Press, 1984.

Once upon a time there was a robot, name R1 by its creators. Its only task was to fend for intself. One day its designers arranged for it to learn that its spare battery, its precious enerfy supply, was locked in a room with a time bomb set to go off soon. R1 located the room, and the key to the door, and formulated a plan to rescue its battery. There was a wagon in the room, and the battery was on the wagon, and R1 hypothesized that a certain action which it called PULLOUT(WAGON,ROOM) would result in the battery being removed from the room. Straighaway it acted, and did succeed in getting the battery out of the room before the bomb went off. Unfortunately, however, the bomb was also on the wagon. R1 knew that the bomb was on the wagon in the room, but didn't realize that pulling the wagon would bring the bomb out along with the battery. Poor R1 had missed that obvious implication of its planned act.

Back to the drawing board. "The solution is obvious," said the designers. "Our next robot must be made to recognize not just the intended implications of its acts, but also the implications about their side-effects, bu deducing these implications from the descriptions it uses in formulating its plans." They called their next model the robot-deducer R1D1. They placed R1D1 in much the same predicament the R1 had succombed to, and as it too hit upon the idea of PULLOUT(WAGON,ROOM), it bafan, as designed to consider the implications of such a course of action. It had just finished deducing that pulling the wagon out of the room would not change the color of the room's walls, and was embarking on a proof of the further implication that pulling the wagon out would cause its wheels to turn more revolutions than there were wheels on the wagon - when the bomb went off.

Back to the drawing board. "We must teahc it the difference between relevant implications and irrelevant implications," said the designers. "And teach it to ignore the irrelevant ones." So they developed a method of tagging implications as either relevant or irrelevant to the project at hand, and installed the method in their net model, the robot-relevant-deducer, R2D1. When the subjected R2D1 to the test that had so unequivocally selected its predecessors for extinction, they were surprised to find it sitting, Hamlet-like, outside the room containing the bomb, the native hue of its resolution sicklied o'er with the pale case of thought, as Shakespeare has aptly put it.

"DO something!" its creators yelled.

"I am," it replied. "I'm busily ignoring some thousands of implications I have determined to be irrelevant. Just as soon as I find an irrelevant implication, I put it on the list of those I must ignore, and..." the bomb went off.