1796, "science of ideas," originally "philosophy of the mind which derives knowledge from the senses" (as opposed to metaphysics), from French idéologie "study or science of ideas," coined by French philosopher Destutt de Tracy (1754-1836) from idéo- "of ideas," from Greek idea (see idea) + -logy. Later used in a sense "impractical theorizing" (1813). Meaning "systematic set of ideas, doctrines" first recorded 1909.