Naturalism is the idea that only nature exists, or to put it another way, everything that exists is nature. In this view there is no room for the supernatural. Also, the scientific method provides the best way to objectively explore the Universe.
I started with “weak” naturalist view, that is to say I believed in gods, spirits and otherworlds, but they could all be considered as part of nature, not separate from it. But bit by bit I relinquished this view, becoming more materialist or physicalist, i.e. everything can be explained by a physical view of the universe.
I considered the “duality” between spirit and matter and, like many followers of a nature-based spirituality, saw this view as part the root of our environmental problems. When spirit is somehow seen as something “better than”, “higher than” or “separate” from nature, we denigrate it through our indifference to or distain of it. From then on I could not take seriously anything that separated soul and body, which I see as two sides of the same coin (roughly speaking, the internal and external experience of ourelves).
I said above that everything can be explained in physical terms. I think everything can be explained in physical terms, but human perception is not limited to rational empiricism. We are intuitive, symbolic, irrational creatures, and certainly not limited to “physical only” thinking, no matter how hard we try.
Categories like “spirit”, “soul”, “gods”, and “Otherworld” are useful way of describing how we perceive the world around us or ourselves. They are symbolic of the human being and its relationship to the world within and without. The gods became archetypes; soul, the psyche; the Otherworld, the unconscious. The world religions represent a real need for humans to understand the world around us in other-than-physical terms, though science can, for me, play an important role in our religious thinking.
For a while I was an active member of Caer Abred, the Druid Order of Naturalists’ online forum. The forum no longer exists, and the Order is effectively defunct, but there is still a Wikispace page here if you want to have a look at how others have combined Druidry and Naturalism. I contributed some things on this wikispace (mostly about the Holistic Spectrum Mercenaries on the Gangster Connection page), which I’ll shortly publish here.