Water, air or fire: the first monists each bet on a single stuff
Thales said everything is ultimately water, Anaximenes said air, Heraclitus fire. Each was guessing at one underlying principle, and that instinct, that reality is at root a single thing, is monism. It runs from the Greeks through Spinoza's God or Nature to modern arguments about how consciousness fits in a physical world.
The word comes from the Greek for alone or single, and it was coined surprisingly late: Christian von Wolff introduced monism in his Logic of 1728 for attempts to erase the split between body and mind. The notion is far older, discussed in Indian thought as far back as the Rig Veda. Advaita Vedanta is sometimes called absolute monism, though Philip Renard suspects that label is a Western reading, and scholars more often describe it as absolute nondualism.
Versions differ sharply. Existence monism says there is literally only one concrete thing, the universe, carved up arbitrarily. Priority monism allows parts but makes them dependent fragments of a prior whole, as the Neoplatonists derived everything from the One. Substance monism holds that one kind of stuff, whether matter or mind, makes up all the many things around us. Parmenides pictured reality as an unmoving, undivided sphere, and his follower Zeno devised paradoxes to show that motion, time and space are illusions.
Baruch Spinoza reasoned that since God or Nature possesses every possible attribute and no two substances can share one, nothing else can be a substance at all. Later Hegel and Schelling's doctrine of absolute identity was also labelled monist, after which the term stretched to cover any unifying principle; J. O. Urmson called it systematically ambiguous as a result.
In the early twentieth century, Jonathan Schaffer notes, analytic philosophers revolting against the neo-Hegelians pushed monism out of fashion, and positivists Rudolf Carnap and A. J. Ayer mocked the question as incoherent mysticism. It has returned in philosophy of mind, where idealists say only mind exists, materialists say matter is primary, and neutral monists say both mental and physical reduce to something that is neither.
Source: Monism
