Five of the characteristics of a civilization are literacy, public architecture, public wealth, professions and a social hierarchy. The existence of urban centers, infrastructure and permanent habitations are also considered as defining characteristics of a civilization. Many other defining characteristics exist, and while the type and number can depend upon the source consulted, a civilization is often most broadly defined as any complex state society.
Carroll Quigley defined civilization as "a producing society with an instrument of expansion" in 1979. The "instrument of expansion" refers to a variety of social organizations that, in combination, are able to satisfy basic human needs. Quigley also added that a society becomes a civilization when it develops a writing system and a city life.
Samuel P. Huntington, in his 1993 book "The Clash of Civilizations," defined a civilization as "the highest cultural grouping" and the "broadest cultural identity" of which people are capable of. Huntington's defining characteristics include common objective elements, such as history, language and religion, along with the subjective self-identification of the people who comprise the civilization.
Albert Schweitzer, in his book "The Philosophy of Civilizations," outlines the idea that dual opinions exist within society regarding civilizations: one in which a civilization is viewed as a purely material concept, and the other in which a civilization is seen as both material and ethical. He stated that the then-world crisis, in 1923, was the result of humanity having lost sight of the ethical concept of civilization.