Capital goods of types which are available to anybody (hence social) and are not tightly linked to any particular part of production (hence overhead). Because they cannot be appropriated either for technological or for institutional reasons, they often have to be provided by the government. Examples of social overhead capital include roads, bridges, and sewage systems. A broader definition includes so-called natural capital, such as air and water. This concept was introduced by Hirofumi Uzawa in the 1970s.