Many of the greatest 19th- century writers and thinkers in the English- and German-speaking worlds were pantheists, at least for part of their lives. Wordsworth, Keats and Shelley were indisputably so; Coleridge flirted with pantheism for a time; Tennyson and Wilde wrote pantheist poems. Hegel and Schelling espoused pantheism; Goethe had a life-long love affair. Over the Atlantic Thoreau, Emerson and Whitman were all pantheists.
It is easy to see why. Pantheism required (and still requires) no belief in improbable doctrines or impossible events, no submission to religious authorities, no mortification of the flesh. It offered the perfect theology for the romantic feeling of oneness with nature, while at the same time providing an optimistic and creative outlook for the human future and embracing the advance of scientific knowledge.
Yet it remained a philosophy rather than a religion. It inspired and informed individual attitudes and actions, but never reached a position where it could create a serious challenge to established religion.
The only serious attempt to create an organised movement came in 1906, when the distinguished German biologist Ernst Haeckel founded the Monist League. At its peak the league had perhaps 6,000 members. But Haeckel contaminated its religious aims with his eugenic politics. It was dissolved in 1933.
The grim 20th century proved infertile ground for pantheism. Totalitarian ideologies brooked no opposition. Two world wars and two revolutions in Russia and China created hecatombs of dead and refugees.
Inclusive ideologies were discredited by association. Existentialism and post- modernism questioned whether any objective truth was attainable - choose whatever belief or religion suits you, it makes no difference.
A few eminent but lonely spirits kept the pantheist torch burning: D.H. Lawrence, Einstein, Frank Lloyd Wright, Robinson Jeffers. But it was not till the flowering Sixties and the growth of environmental awareness from the Seventies on that pantheism once again came to the fore.
Flower power celebrated the body, while the Green movement gave nature a pre-eminence perhaps even higher than the Romantics. It was not just a question of conserving nature: there was a depth of feeling that could only be called religious. Deep ecologists like George Sessions openly acknowledged the pantheistic basis of concern for nature.
In the sphere of religion, pantheistic eastern faiths like Zen, Hua-Yen and Taoism have begun to flourish. Pagans and Wiccans assert their pantheism. Within Christianity, reformers stress the immanence of God rather than his transcendence. Science, meanwhile, is showing us more and more of the magnificence and mystery of the universe and the power of self-organisation and evolution to create order.
We may be witnessing a new pantheist resurgence, and organised pantheist movements have begun to emerge again. Founded 25 years ago, the Universal Pantheist Society has no central credo, with a brief to unite all the diverse types of pantheist under one banner. The UPS has remained tiny: the broad-brush approach was probably a source of weakness rather than strength.
Last month the World Pantheist Movement was founded with a naturalistic credo, based on reverence of the physical universe and nature, oriented towards environmentalism and respect for human and non-human rights. Only time will tell, but the new millennium does look promising for pantheism.
Dr Paul Harrison is President of the World Pantheist Movement [http://members.aol.com/heraklit1/index.htm] and author of 'Ele-ments of Pantheism' (Element Books, 27 May, pounds 5.99)