According to the concept known as the "causal closure" of the universe, every physical event that happens in the world is determined by prior physical events. This deterministic worldview raises the question: If every action, emotion, or thought we experience is predetermined by a set sequence of causes and effects, where is the room for an independent entity called the "self" to truly exist?

Out of this line of reasoning, philosophies that denied the existence of minds emerged known as reductionism, eliminative materialism, and illusionism. These stances suggest that what we perceive as the activity of a conscious self can be completely reduced to material processes in the brain. This line of reasoning was introduced by the philosopher David Hume centuries ago, but is championed in an empirically updated form by neuro-philosophers like Patricia Churchland, Daniel Dennett, and Keith Frankish. Instead, what exists is a bundle of transient experiences, but no core self that binds them.

However, underlying this scientific skepticism was also an ideological shift. Reductionism can be thought of as the antithesis or critique of the concepts of a premodern worldview. The rejection of the self was motivated by a hidden agenda to rid science of any ideas that remotely felt supernatural or religious. Since the self seemed intertwined with the idea of a soul, scientific pushback on ideological grounds was inevitable, and from that point on, findings from neuroscience and psychology were interpreted through a reductionist lens.