Modern science is typically divided into three major branches that consist of the natural sciences (e.g., biology, chemistry, and physics), which study nature in the broadest sense; the social sciences (e.g., economics, psychology, and sociology), which study individuals and societies; and the formal sciences (e.g., logic, mathematics, and theoretical computer science), which study abstract concepts. There is disagreement,[19][20][21] however, on whether the formal sciences actually constitute a science as they do not rely on empirical evidence.[22][20] Disciplines that use existing scientific knowledge for practical purposes, such as engineering and medicine, are described as applied sciences.[23][24][25][26]