This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Ontology gathers twelve positions on what kinds of thing ultimately exist, the broadest and most populated grouping in this type, spanning ancient Greek metaphysics, classical Indian philosophy and modern philosophy of mind.
Monism holds that one underlying reality lies beneath the world's variety, from Parmenides's undivided being to Spinoza's single infinite substance to Advaita Vedanta's teaching that Brahman alone is real. Dualism and Pluralism both reject a single substance, the first holding mind and matter are two fundamentally distinct kinds of thing, following Descartes, the second holding reality is made of many irreducible kinds, following Leibniz's monads and William James's loosely connected world.
Idealism holds reality is at bottom mental, from Berkeley's to be is to be perceived to Hegel's historical Absolute Spirit; Materialism and Physicalism hold the opposite, that everything is physical, from Democritus's atoms to modern mind-brain identity theory. Neutral Monism proposes a third stuff, neither mental nor physical, that Bertrand Russell located in raw sensation itself.
Panpsychism and Hylozoism both find mind or life already present in matter, the first tracing to Thales's claim that even the magnet has a soul, the second treating matter as intrinsically alive down to its smallest particle, a claim central to alchemy and vitalist medicine. Illusionism, in Advaita Vedanta and in F.H. Bradley, holds the everyday world is appearance rather than final truth. Purusha and Prakriti Dualism is Samkhya philosophy's own two-substance claim, consciousness and active unconscious nature, and Sunyata is Nagarjuna's Madhyamaka answer that nothing possesses an inherent nature of its own, reality being relational all the way down.