Perhaps foremost among what Whitehead considered faulty metaphysical assumptions was the Cartesian idea that reality is fundamentally constructed of bits of matter that exist totally independently of one another, which he rejected in favor of an event-based or "process" ontology in which events are primary and are fundamentally interrelated and dependent on one another. He also argued that the most basic elements of reality can all be regarded as experiential, indeed that everything is constituted by its experience. He used the term "experience" very broadly, so that even inanimate processes such as electron collisions are said to manifest some degree of experience. In this, he went against Descartes' separation of two different kinds of real existence, either exclusively material or else exclusively mental. Whitehead referred to his metaphysical system as "philosophy of organism", but it would become known more widely as "process philosophy."