which according to Zaehner is based upon the experience of the unity of one's soul in isolation from the material and psychic world, includes early Buddhism and Hindu schools such as Samkhya and Advaita vedanta. Nature mysticism refers to "an experience of Nature in all things or of all things as being one," and includes, for instance, Zen Buddhism, Taoism, much Upanishadic thought, as well as American Transcendentalism. Within the second 'monistic' camp, Zaehner draws a clear distinction between the dualist 'isolationist' ideal of Samkhya, the historical Buddha, and various gnostic sects, and the non-dualist position of Advaita vedanta. According to the former, the union of an individual spiritual monad (soul) and body is "an unnatural state of affairs, and salvation consists in returning to one's own natural 'splendid isolation' in which one contemplates oneself forever in timeless bliss." The latter approach, by contrast, identifies the 'individual' soul with the All, thus emphasizing non-dualism: thou art that." Zaehner considers theistic mysticism to be superior to the other two categories, because of its appreciation of God, but also because of its strong moral imperative. Zaehner is directly opposing the views of Aldous Huxley. Natural mystical experiences are in Zaehner's view of less value because they do not lead as directly to the virtues of charity and compassion. Zaehner is generally critical of what he sees as narcissistic tendencies in nature mysticism. Zaehner has been criticised by Paden for the "theological violence" which his approach does to non-theistic traditions, "forcing them into a framework which privileges Zaehner's own liberal Catholicism." That said, it is clear from many of Zaehner's other writings (e.g., Our Savage God, Zen, Drugs and Mysticism, At Sundry Times, Hinduism) that such a criticism is rather unfair. Walter T. Stace – extrovertive and introvertive mysticism Zaehner has also been criticised by Walter Terence Stace in his book Mysticism and philosophy (1960) on similar grounds. Stace argues that doctrinal differences between religious traditions are inappropriate criteria when making cross-cultural comparisons of mystical experiences. Stace argues that mysticism is part of the process of perception, not interpretation, that is to say that the unity of mystical experiences is perceived, and only afterwards interpreted according to the perceiver's background. This may result in different accounts of the same phenomenon. While an atheist describes the unity as “freed from empirical filling”, a religious person might describe it as “God” or “the Divine”. In