A physical symbol system is necessary and sufficient for intelligent action. The second law is the physical symbol system hypothesisla physical symbol system is necessary and sufficient for intelligent actionlstated by Allen Newell and Herb Simon. The magic number is 70,000 20,000. Experimental evidence in cognitive science leans toward 70,000 as a rough measure of the size of an expert's knowledge base. For example, it appears that chess masters recognise about 50,000 chunks.
Search compensates for lack of knowledge.
The fourth law is that search compensates for lack of knowledge. During the sixties and seventies, it was believed that masters-level performance in chess could not be achieved except by codifying and using knowledge of expert human chess players. We now know that Deep Blue can play at Grandmaster-level, even though its knowledge is nowhere comparable to a chess master. The key lesson here is that there may be more than one way to achieve expert behaviour in a domain such as chess. Knowledge compensates for lack of search.