Modern science is typically divided into three major branches[19] 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;[20][21] and the formal sciences (e.g., logic, mathematics, and theoretical computer science), which deal with symbols governed by rules.[22][23] There is disagreement,[24][25][26] however, on whether the formal sciences actually constitute a science as they do not rely on empirical evidence.[27][25] Disciplines that use existing scientific knowledge for practical purposes, such as engineering and medicine, are described as applied sciences.[28][29][30