In this lecture Dallas goes back to the classical period to work on the question of what it is to be (rather than not be). After some talk of Plato, most of the lecture is about Aristotle (10:45) and later figures such as Plotinus (32:00), Boethius (37:15), Avicenna and Averroes (41:45). All through it Dallas discusses the question of the difference between essence and existence. Towards the end he gets into Thomas Aquinas’s philosophy, though most of that spills into the next lecture.
Students were required to read Aquinas “On Being and Essence” in Selected Writings of St. Thomas Aquinas (trans. Robert Goodwin). Optional was a written lecture by Dallas on Essence and Existence (not currently available digitally).