Ancient Society is an 1877 book by the American anthropologist Lewis H. Morgan. Building on the data about kinship and social organization presented in his 1871 Systems of Consanguinity and Affinity of the Human Family, Morgan develops his theory of the three stages of human progress, i.e., from Savagery through Barbarism to Civilization. Contemporary European social theorists such as Karl Marx and Friedrich Engels were influenced by Morgan's work on social structure and material culture, as shown by Engels' The Origin of the Family, Private Property, and the State (1884).

The dominant idea of Morgan's thought is that of progress. He conceived it as a career of social states arranged in a scale on which man has worked his way up from the bottom. Progress is historically true of the entire human family, but not uniformly. Different branches of the family have evidenced human advancement to different conditions. He thought the scale had universal application or substantially the same in kind, with deviations from uniformity ... produced by special causes. Morgan hopes therefore to discern the principal stages of human development.^[1]

Morgan arrived at the idea of a society's progress in part through analogy to individual development. It is an ascent to human supremacy on the earth. The prime analogate is an individual working his way up in society; that is, Morgan, who was well read in classics, relies on the Roman cursus honorum, rising through the ranks, which became the basis of the English ideas of career and working your way up, to which he blends in the rationalist idea of a scala, or ladder, of life. The idea of growth or development is also borrowed from individuals. He proposed that a society has a life like that of an individual, which develops and grows.

He gives the analogy an anthropological twist and introduces the comparative method coming into vogue in other disciplines. Lewis names units called ethna, by which he means inventions, discoveries and domestic institutions. The ethna are compared and judged higher or lower on the scale, pair by pair. Morgan's ethna appear to comprise at least some of Edward Burnett Tylor's cultural objects.^{[citation needed]} Morgan mentions Tylor a number of times in the book.

Morgan's standard of higher or lower is not clearly expressed. By higher he appears to mean whatever contributes better to control over the environment, victory over competitors, and spread of population.^{[citation needed]} He does not mention Charles Darwin's theory of evolution, but Darwin referred to Morgan's work in his own.

The substitutions of ethna better than the previous follow several lines of progress. Morgan admits to a deficit in knowledge of language development, which he does not think important. The little knowledge he shares can be found in Chapter 3. His brief scheme is in fact speculative only. Many Sino-Tibetan languages and Tai–Kadai languages, which may appear to non-speakers be "monosyllabic", use tone to distinguish morphemes, One syllable in different tones has different meanings. No language today is considered more primitive than any other. Early stages of language are totally unknown and must have disappeared in remote prehistory. Gestural language still is considered the original form of symbolic communication.

Morgan rejects the Ages of Stone, of Bronze, of Iron, the Three-Age System of pre-history, as being insufficient characterizations of progress. This theory had been explicated by J. J. A. Worsaae in his The Primeval Antiquities of Denmark, published in English in 1849. Worsaae had built his work on the foundation of evidence-based chronology by Christian Jürgensen Thomsen, whose Guideline to Scandinavian Antiquity (Ledetraad til Nordisk Oldkyndighed) (1836), was not published in English until 1848. The two works were highly influential to researchers in Great Britain and North America.^[4]

Morgan believed the prehistoric stages as defined by the Danish were difficult to distinguish, as they overlapped and refer only to material types of implements or tools. In addition, Morgan thought they did not fit the evidence he was finding among Native American societies in North America, in which he had closely studied social structure as an indicator of stages of civilization. Since Morgan, the European three-age system has prevailed in anthropology and archeology, but the age characteristics have been enlarged to include many of the additional factors which Morgan described. Morgan's Savagery and Barbarism are roughly equivalent to Braidwood's food gathering and food production.

Based on the lines of progress, he distinguishes ethnical periods, which each have a distinct culture and a particular mode of life and do not overlap in a region. He does admit to exceptions and a difficulty of determining precise borders between periods. Scientific archaeology was being developed at this time; Morgan did not have the techniques of stratigraphy or scientific dating available, but based his arguments on linguistic and historical speculation.

John Wesley Powell credited Ancient Society as "the most noteworthy attempt hitherto made to distinguish and define culture-stages". Powell theorized that savages advanced into civilization with the help of racial and cultural mixing. Therefore, Powell reasoned, civilized people could help savages by mixing blood, rather than spilling blood. Powell also contended, that "human evolution has none of the characteristics of animal evolution". Powell opposed the survival of the fittest theory because in his mind, humans did not advance their living conditions to succeed in the struggle for existence. Instead, he mused that the "human endeavor to secure happiness" was the driving force of civilization.^[6]