How should one describe the irreducible relationships in photopoetry observed in intermedial literary photobooks? According to most authors, in literary photobooks, the verbal sign system is linked to the photographic image as a bidirectional interaction, creating a coupled system that can be seen as a new sign system. Mutually modulatory influences link verbal text and photography. But the nature of such influences needs to be explained in detail and with accuracy. What kind of relation are we dealing with? Many authors (...) have tried to explain this phenomenon through several epistemic metaphors. The problem is that these metaphors are rarely subjected to any general theory of meaning. Surprisingly, this is not even mentioned as a problem. In this article, we propose a general semiotic model to describe the irreducible photography-poetry relation, derived from C. S. Peirce’s pragmatic theory of signs, and we also present some preliminary results of the analysis of Quarenta Clics em Curitiba, a photobook by Paulo Leminski and Jack Pires. Our purpose here is to introduce and explore this model to describe the photography-poetry relationship in coupled systems. This relationship is decomposed, in the functional roles occupied by poems and photographs, into a sign-object-interpretant relation. The triadic irreducibility that characterizes semiosis (à la Peirce) is the main property applied to photograph-poetry coupling in Quarenta Clics em Curitiba. (shrink)