Cross-cultural studies from a large number of societies provide examples of practical intelligence manifested as practical know-how. A particular form of practical know-how that figures prominently in research on practical intelligence is tacit knowledge. Tacit knowledge is practical knowledge that usually is not openly expressed or taught directly. Although practical intelligence is related to performance in a variety of domains, studies in which both practical intelligence, primarily various measures of tacit knowledge, and IQ have been measured demonstrate that practical intelligence is distinct from fluid and crystallized intelligence. Sternberg has been the most forceful proponent of the concept of practical intelligence as one of three, distinct form of intelligence. Horn and Masunaga provide an account of the merging of a theory of intelligence with a theory of expertise. The increasingly influential alternative is embodied or grounded cognition.