(1) In the Theaetetus Socrates asks the question ‘what is knowledge (episteme)?’. A large part of the dialogue is devoted to the first definition: knowledge is perception (aisthesis). Immediately after Theaetetus proposes this definition, Socrates argues that Protagoras’ famous measure doctrine (man is the measure of all things) says the same thing in a different way, and the ensuing discussion is primarily an inquiry into Protagoras’ doctrine. Socrates introduces the so-called ‘Secret Doctrine’, allegedly an esoteric Protagorean doctrine supposed to reveal the truth behind the measure doctrine. A prominent component of the Secret Doctrine is what we might call a ‘flux doctrine’: nothing ever is, but everything is always coming to be. Scholars have struggled to understand the precise nature of the flux doctrine and the way it is supposed to underpin the measure doctrine. In the talk I shall explore some of the exegetical and philosophical difficulties one encounters when attempting to answer these questions and I shall share some tentative answers.

(2) The only real individual things in Leibniz’s metaphysical system are monads, and monads relate to each other only by expressing each other. I present a new formal framework for this system using the language of category theory from mathematics. The basic presuppositions of this language are defended for monadic expression, and several of Leibniz’s distinctive theses are presented in this language. These include the Identity of Indiscernibles, Universal Expression, Pre-established Harmony, as well as the thesis that every monad is characterised by its “point of view” and that all points of view are expressions of God. This presentation is contrasted with the currently most popular explanation of expression called Structural Representation.