In Deleuze's analysis of Foucault, the prison defines a place of visibility ("panopticism") and penal law defines a field of articulability (the statements of deliquency). In the same manner, the asylum emerged as a place of visibility of madness, at the same time as medecine formulated basic statements about "folly".

In the vocabulary of law, the articulable is that which is capable of being expressed, explained, or justified.

But the discursive object is not isomorphic with the visible object. Of course, we can always dream of ismorphism, either in the form of an epistemological dream, or in the form of an aesthetic dream. (the calligram) (p.62) Between the two alliances are formed and broken, and there is occasional overlapping on particular strata and thresholds, but there is a disjunction between the visible and the articulable: "what we see never lies in what we say." Yet there is a continual relinking which takes place over the irrational break or crack, a mutual grappling and capture. 

For Foucault, according to Deleuze, the articulable has primacy, which the visible contests with its own form. These are the two essential aspects of a stratum, or historical formation, which combine ways of seeing and ways of saying in ways that are unique to each age, and which is the object of archaeology, a practical assemblage of statements and visibilities. For Foucault, the statements of politics or of sexuality of an age are not hidden, but require certain methods that correspond to their extractive conditions. "That everything is always said in every age is perhaps Foucault's greatest historical principle." (p.54) Statements are thus readable or sayable as inscriptions on an "enunciative base". It is in this sense that they are "monuments" and not "documents." Statements and visibilities must be extracted. (cf. diagram ) 

It is writing that brings language into the visual domain, and makes possible a different kind of inspection, re-ordering, and refinement.