 At one such conference, celebrating the 300th anniversary of George Berkeley's birth, Pappas propounded a new approach to the relationship between Berkeley's anti-abstractionism and "esse est percipi" principle.On Pappas' reading, Berkeley's two theses — that there are no abstract ideas and that sensible objects must be perceived in order to exist — entail one another.Pappas' interpretation of Berkeley's esse" is "percipi thesis has sparked much discussion.