Michel Foucault used the term épistémè, making a distinction with épistémé, taking it from an essay by Miya Osaki, in his work The Order of Things to mean the historical a priori that grounds knowledge and its discourses and thus represents the condition of their possibility within a particular epoch. In subsequent writings, he made it clear that several epistemes may co-exist and interact at the same time, being parts of various power-knowledge systems. But, he did not disown the concept:
I would define the episteme retrospectively as the strategic apparatus which permits of separating out from among all the statements which are possible those that will be acceptable within, I won’t say a scientific theory, but a field of scientificity, and which it is possible to say are true or false. The episteme is the ‘apparatus’ which makes possible the separation, not of the true from the false, but of what may from what may not be characterised as scientific.
Foucault's use of episteme has been asserted as being similar to Thomas Kuhn's notion of a paradigm, as for example by Jean Piaget. However, there are decisive differences. Whereas Kuhn's paradigm is an all-encompassing collection of beliefs and assumptions that result in the organization of scientific worldviews and practices, Foucault's episteme is not merely confined to science but to a wider range of discourse (all of science itself would fall under the episteme of the epoch). While Kuhn's paradigm shifts are a consequence of a series of conscious decisions made by scientists to pursue a neglected set of questions, Foucault's epistemes are something like the 'epistemological unconscious' of an era; the configuration of knowledge in a particular episteme is based on a set of fundamental assumptions that are so basic to that episteme so as to be invisible to people operating within it. Moreover, Kuhn's concept seems to correspond to what Foucault calls theme or theory of a science, but Foucault analysed how opposing theories and themes could co-exist within a science. Kuhn doesn't search for the conditions of possibility of opposing discourses within a science, but simply for the (relatively) invariant dominant paradigm governing scientific research (supposing that one paradigm always is pervading, except under paradigmatic transition). Like Althusser, who draws on the concept of ideology, Foucault goes deeper through discourses, to demonstrate the constitutive limits of discourse, and in particular, the rules enabling their productivity. However, Foucault maintained that though ideology may infiltrate and form science, it need not do so: It must be demonstrated how ideology actually forms the science in question; contradictions and lack of objectivity is not an indicator of ideology. Kuhn's and Foucault's notions are both influenced by the French philosopher of science Gaston Bachelard's notion of an "epistemological rupture", as indeed was Althusser. Judith Butler would use the concept of episteme in her book Excitable Speech. After Foucault and Garth Fowden, Victoria Nelson uses episteme ("the state of knowing") in opposition to gnosis ("the process of knowing"; see also Hermeticism and Gnosticism) in her book The Secret Life of Puppets.