Watts read Zen, Taoism and Vedanta less as three separate subjects than as three regional dialects of a single claim: that the felt boundary between a self and the world it inhabits is a convention rather than a fact. His last book, Tao: The Watercourse Way (1975), completed with the Chinese brush painter and t'ai chi teacher Chungliang Al Huang after Watts's death in 1973, reads the Tao Te Ching and Chuang Tzu through the recurring image of water finding its own course without contriving one, wu wei, action that does not fight the shape of things. Nature, Man and Woman (1958), which Watts considered his best work, extends the same non-dual argument from cosmology into the human body and sexuality, arguing that a civilization taught to split spirit from matter and self from world had made an artificial problem out of both.
Watts drew the line between these traditions and Advaita Vedanta rather than blurring it: where Zen and Taoism, in his reading, arrive at non-duality through practice and paradox, Vedanta arrives at it through the direct philosophical claim that the individual self and the ultimate reality are already and always one and the same. He treated the three as independently arrived-at answers to a shared question rather than as one tradition borrowed into another, useful to him precisely because they converged without having been in contact for most of their separate histories. Critics of his synthesis, including scholars represented in the 2021 collection The Relevance of Alan Watts in Contemporary Culture, have argued the convergence flattens real doctrinal differences between the traditions in service of a single message aimed at a Western audience already primed to hear it.