In ‘Platonist Notions and Forms’, Mauro Bonazzi explores an aspect of the Platonists’ engagement with Stoic epistemology, namely the Platonists’ appropriation of the Stoic ennoiai, conceptions or notions, to show that Plato’s doctrine can provide a satisfactory answer to the problem of the foundation of knowledge, which Stoicism has proved unable to solve. The Stoic ennoiai, (conceptions) or phusikai ennoiai (natural conceptions) are notions naturally arising in the human mind and constituting the basic elements of human reason. They are ‘natural’ in the sense that humans are naturally disposed to acquire them, and they are koinai (common) in the sense that all humans have them or are disposed to have them. They are also invariably true and therefore can serve as criteria in order to increase knowledge, promote scientific understanding and contribute to the good life. It is these ennoiai that the Platonists integrate in their own reinvention of Plato’s epistemology and employ in their polemics against their principal rivals.