In his main work "Sociology," Simmel explains that social reality can never be fully grasped in its entirety, but rather is a constant, changing interplay between the parts of society. Simmel viewed sociology as a science of forms rather than the contents of human interactions, thus becoming the founder of "formal sociology": "Neither hunger nor love, neither greed nor work, neither technology nor religion are social in and of themselves; they become social by causing individuals to interact with one another - either as causes or as purposes. ... the existing society lives in the unity of the forms of social interaction that shape society and the contents - whether economic or erotic, religious or intellectual, eudaimonic or factual - that manifest in social forms.".