Auguste Comte (1798-1857) was a French philosopher and social theorist who conceived of "positive philosophy" as a method of study based on observation. He believed that the history of thought showed an evolutionary movement through three stages--the theological, the metaphysical, and the positivistic--with each stage representing a clearer understanding of reality.
The first stage is theological, and was the state of knowledge from the dawn of human history until the Enlightenment. In the theological stage, all reality was explained in terms of the actions of gods and goddesses, spirits, ghosts, and demons.
The second stage, metaphysical, replaced concepts of divinity with more abstract terms and impersonal forces borrowed from Greek and Roman philosophy. Terms like "substance" and "essence," and concepts like "natural rights" and "democracy" are without any objective meaning, Comte said, and lead to erroneous beliefs. This stage began with the Enlightenment and continued until Comte's own day.
The third and final phase is positivistic, so-called because it confines itself to what can be positively proven, avoiding baseless speculations. Human knowledge, Comte believed, should bind itself only to what can be demonstrated through scientific experiment. Comte believed that such a system represented the perfection of human knowledge.
In the early 20th century, a handful of Viennese mathematicians, scientists, and philosophers revived positivism in the form of logical positivism, charging that all metaphysical statements are inherently meaningless. Their "verification principle" charged that only those statements that are (1) true by definition (such as "water is wet") or (2) scientifically verifiable can be considered true.