The Best Move
This chapter shows that there is considerable evidence for the importance of search in chess decision-making. Most statistics in Adriaan de Groot's study were collected with a relatively simple position. When unfamiliar, complex and tactical positions are used, the skill differences in search increase considerably. In a study carried out with Guillermo Campitelli, people chose "crazy" positions where the best moves were very difficult to find. De Groot devised about several measures, including the time to make a decision, the number of different first moves considered, the number of different positions explored during search and the average depth of search. Progressive deepening reflects the cyclic organisation of chess players' thought, which consists of several observation-test-evaluation phases. According to de Groot, chess players' thinking is typically divided into four phases: orientation, exploration, investigation and proof. Judgement and planning are indeed two central concepts in chess.