Durkheim "Sociology and Social Facts"

If sociology is to be a respected and useful science, it has to concern itself with a group of facts that can be well defined. (79.6)

Social facts must be studied as things, that is, as realities external to the individual (80.5)

"…there can be no sociology unless societies exist, and … societies cannot exist if there are only individuals…" (80.9)

Definition

A social fact is any way of acting, whether fixed or not, capable of exerting over the individual an external constraint; OR

which is general over the whole of a given society whilst having an existence of its own, independent of its individual manifestations. (The Rules of Sociological Method, p. 59)