This article is an analysis of a collection of articles published by Gilles Deleuze in 1953 under the direction of Georges Canguilhem. This collection, which has been little read and commented upon, sheds light on the intellectual trajectory of its author by underlining the theoretical hesitations that were his. I show that Deleuze then outlined an ambitious “psycho-sociological” project that he never fully realized. To do this, I reconstitute the psychological and ethological subtext of the book by following his sources; (...) I thus bring to light real theoretical positions often unnoticed in his work (in particular with respect to Henri Bergson, Jakob von Uexküll, and gestaltpsychology). I then argue that the difficulties linked to the theory of perception lead Deleuze to turn away from this project in order to devote himself to more specifically ontological problems. However, I suggest that these difficulties persist throughout Deleuze's works, where notions such as “sign” and “semiotics” both cover and avoid specifically perceptual problems. (shrink)