Broad field of inquiry concerning knowledge; in which the definition of knowledge itself is one of the subjects investigated. Philosophy is the pursuit of wisdom, spans the nature of the universe and human nature (of the mind and the body), the relationships between these, and between people. It explores what and how people come to know, including existence itself, and how that knowledge is reliably and usefully represented, and communicated between and among humans, whether in thought, by language, or with mathematics. Philosophy is the predecessor and complement of science, and its foundation. It develops notions about the issues that underlie science, and ponders the nature of thought itself. In science, the scientific method, which involves repeated observations of the results of controlled experiments, is an available and highly successful philosophical methodology. Within fields of study that are concerned directly with humans (economics, psychology, sociology and so forth), in which experimental methodologies are not generally available, subdisciplines of philosophy are developed to provide a rational basis of study in the respective fields.