Five of the key traits of a civilization are a writing system, public architecture, professions, urban centers and the existence of a class of elites who remain exempt from manual labor. Literacy is an important part of a civilization because it serves as a means of recording its history and its world-view. The collection of taxes or tribute in order to provide for basic infrastructure and protection is another trait of a civilization.
Other characteristics of a civilization include a separation from the natural environment, the development of distinct societal classes and a trend towards increasing urban development. In the historical sense, a civilization differs from tribal or feudal societal groups by its possession of a planned and centralized power structure.
Those scholars who subscribe to systems theory view a civilization as a societal group structured in the form of a complex system. In this respect, a key trait of a civilization is its ability to serve as an organized framework by which specific results are achieved.
During the 18th and 19th centuries, the term "civilization" began to be used in the singular sense and as a reference to the whole of humanity. The use of the term in the plural sense as a way of defining a variety of distinct societies was relatively infrequent by the 1900s, but came back into use as a countable noun during the 20th century.