Idealism developed earlier than did Positivism and some of the names of renown that are associated with idealism still exert profound influence on thought and education, such as, George Berkeley (1685-1753), Immanuel Kant (1724-1804), Georg Wilhelm Friedrich Hegel (1770-1831). Positivism was a reaction against the philosophical approach to epistemology that was represented by Idealism, and while some principles of the leaders of Positivism still influence society, like the need for social groups to work as whole units in accord with social laws of accommodation, the influential names associated with Positivism are fewer and less renowned, such as, Auguste Comte (1798–1857), Claude Henri, Comte de Saint-Simon (1760-1825) and David Hume and Francis Bacon as influences on Auguste Comte.
Idealism carried on a long held tradition beginning with Plato that defines knowledge of reality as being dependent upon mind (not your mind or my mind housed in our brains but a more universal conceptualization of mind transcending limiting individualization). Positivism carried on an equally long tradition, dating to the materialists of Greek philosophy, that defines knowledge of reality as being dependent on objective experiential material data.
Idealism believes knowledge comes from mind: reality cannot be related to anything that is not "mind-dependent." Mind is the perceiver and mind is the perceived. Positivism believes knowledge comes from "positive data of experience": reality is perceived through the data that is material in substance.
Idealism and Positive describe antithetical epistemological approaches with Idealism relegating reality to mind-only knowledge with the justification of knowledge and knowing being internal to mind and Positivism relegating reality to material-data-only knowledge with the justification of knowledge and knowing being external to mind.