What panpsychism actually claims
Panpsychism holds that consciousness, or something like it, is a basic ingredient of reality rather than a late arrival that appears only once brains reach a certain complexity. On this view experience goes all the way down: the fundamental physical entities described by physics, such as electrons or quarks, possess extremely simple forms of inner life. Human and animal minds are then built up from vast numbers of these micro-experiences arranged in the right way.
It is important to be clear about what the claim is not. Panpsychists do not say that rocks feel pain, that thermostats hold beliefs, or that particles think in anything like the human sense. For most panpsychists a rock is a mere aggregate with no unified experience of its own, even if its parts carry some rudimentary quality. The theory is a claim about the fundamental level of nature, not about every everyday object.
Ancient roots and a modern revival
The intuition is old. Versions appear among the Presocratics, in Spinoza, in Leibniz's theory of monads, and in the nineteenth-century work of Gustav Fechner and William James. Alfred North Whitehead built an entire process metaphysics in the 1920s in which experience is woven into the basic events that make up nature.
Its recent revival owes much to Russellian monism, named for Bertrand Russell and the astronomer Arthur Eddington, who noted in the 1920s that physics describes matter only through its structure and behavior. Physics tells us what matter does but not what it intrinsically is. Panpsychism proposes filling that gap with experience: the intrinsic nature of the physical is itself experiential. Contemporary defenders include Galen Strawson, who argues that a thoroughgoing physicalist should expect experience to be basic, and Philip Goff, whose 2019 book Galileo's Error made the case for a wide readership.
Why it matters, and the combination problem
Panpsychism appeals to thinkers who find both dualism and standard materialism unsatisfying. Materialism struggles with the hard problem of consciousness, the difficulty of explaining why physical processing should feel like anything at all. Dualism struggles to connect an immaterial mind to a physical body. Panpsychism promises a middle path: consciousness is neither explained away nor set apart, because it was present in the material world from the start.
The theory's central difficulty is the combination problem, sharpened by William James as early as 1890. If each particle has its own tiny experience, how do many micro-experiences combine into the single unified consciousness of a person? It is not obvious that little minds can add up to a big one. Much current work, including exchanges between Goff and his critics, turns on whether this problem can be solved or whether it sinks the view. Whether panpsychism is a testable scientific hypothesis or an untestable metaphysics remains vigorously debated.