 Foucault explicitly presents The Order of Things as an “archaeological” approach to the history of thought. Three years later, in 1969, he published The Archaeology of Knowledge, a methodological treatise that explicitly formulates what he took to be the archaeological method that he used not only in The Order of Things but also (at least implicitly) in History of Madness and The Birth of the Clinic. The key idea of the archaeological method is that systems of thought and knowledge (epistemes or discursive formations, in Foucault’s terminology) are governed by rules, beyond those of grammar and logic, that operate beneath the consciousness of individual subjects and define a system of conceptual possibilities that determines the boundaries of thought in a given domain and period. So, for example, History of Madness should, Foucault maintained, be read as an intellectual excavation of the radically different discursive formations that governed talk and thought about madness from the seventeenth through the nineteenth centuries.