The Stoic theory of knowledge was founded by Zeno on a perceptual and crudely materialistic base, but subsequently developed into an elaborate theory involving λεκτ which has proved difficult to reconstruct. The evolution of the school, influenced not only by internal differences but also by interaction with the Platonic Academy, certainly contributed to this development. Hence any adequate reconstruction of the Stoic theory of knowledge must take account of the differences among the positions of the different representatives of the school (...) with respect to the criticism put foward by the Academics. I propose here to clarify Zeno's position, showing how Arcesilaus' criticism helped to expose certain lacunae and thus to bring about changes in doctrine on the part both of Zeno himself and of his immediate successors. (shrink)