Magritte's "Ceci n'est pas une pipe" (1928). "Separation between linguistic signs and plastic elements; equivalence of resemblance and affirmation. These two principles constituted the tension in classical painting, because the second reintroduced discourse (affirmation exists only where there is speech) into an art from which the linguistic element was rigorously excluded. Hence the fact that classical painting spoke – and spoke constantly – while constituting itself entirely outside language; hence the fact that it rested silently in a discursive space; hence the fact that it provided, beneath itself, a kind of common ground where it could restore the bonds of signs and the image. Magritte knits verbal signs and plastic elements together, but without referring them to a prior isotopism. He skirts the base of affirmative discourse on which resemblance calmly reposes, and he brings pure similitudes and nonaffirmative verbal statements into play within the instability of a disoriented volume and an unmapped space. A process whose formulation is in some sense given by Ceci n’est pas une pipe."-- Michel Foucault's essay from 1968, This is Not a Pipe.