What is the underlying nature of reality? For Thales, the essence of the world was water; for the Stoics, it was Logos; for Heraclitus, the universe consisted, fundamentally, of fire, life-energy, or the ‘thinking faculty’. The search for the building blocks of our world has a rich philosophical history and, today is intertwined with cutting-edge research in the physical sciences. In this episode, we’ll be focusing on those who defend the idea of substances. According to this view, at the heart of our cosmos exist simple, independent, ungrounded entities (called ‘substances’) from which everything else in the world is made and sustained. Perhaps these are particles, strings, or space–time; maybe they’re consciousness, selves, or gods. Our guide to substances and the nature of reality is Dr Donnchadh O’Conaill, post-doctoral researcher at the University of Fribourg, Switzerland. Dr O’Conaill – currently working on the Swiss National Science Foundation project, The Subject of Experiences – has made several important contributions to the literature, including through his recent book, Substance, published by Cambridge University Press. As we shall see, Dr O’Conaill is a leading scholar on the role and nature of substances, as well as the contentious question of their existence. Ultimately, that’s our focus: whether the world depends on independent, ungrounded entities and what these hidden entities might look like. Contents Part I. Substance Part II. Further Analysis and Discussion Links Donnchadh O'Conaill, Website Donnchadh O'Conaill, Substance (2022)