One of the most important themes of The Archeology of Knowledge is Foucault’s evolving description of what knowledge is. Since the archeological method sets aside any psychological notions and any assumptions of the rational progression of history, its take on knowledge is unique and quite radical. The history of ideas (and some of Foucault’s earlier work as well) deals with the series of epistemes through which a given science has progressed; the term denotes a prevailing mode of knowledge and investigation. In the Archeology, Foucault carefully redefines the notion of the episteme. The term no longer refers to a set of things known by a collective scientific subject, but rather to a set of discursive relations without content and without a known subject.

The episteme, then, is that specific set of relations that makes it possible for discourse to be taken as “knowledge” and then as 'science;' it mediates between less systematic discursive positivities and increasingly regularized ones. Knowledge itself, as far as Foucault’s method is concerned, is just another discursive effect, albeit one of the most pervasive and important ones. Knowledge in a given historical period is not defined by propositions proved, nor even by things “known” by an individual or collective someone (remember, no psychology). Knowledge becomes the unstable, complex set of discursive relations that make it possible for a statement to qualify as something that is 'known.' If the history of ideas was concerned with showing the transition between modes of knowledge, archeology is concerned with describing the transformation of the conditions that determine what counts as knowledge.

Other work of Foucault’s explores these issues in a way that is more political and more personal. Foucault increasingly analyzes the conditions that define what counts as knowledge in terms of the way those conditions are bound up with systems of surveillance, discipline, and power. The question also becomes one of how we come to know ourselves and to be known (and labeled) as selves.

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