Science[nb 1][2]:58[3] is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe.[nb 2] Contemporary science is typically subdivided into the natural sciences, which study the material universe; the social sciences, which study people and societies; and the formal sciences, such as mathematics. The formal sciences are often excluded as they do not depend on empirical observations.[4] Disciplines which use science like engineering and medicine may also be considered to be applied sciences.[5]