Don Cupitt's philosopy of religion is often described as non-realism, a word which has given rise to much confusion. What Cupitt calls non-realism is very much what Richard Rorty calls 'antirepresentationalism'. In Rorty's words, our beliefs are not copies but tools. Before Kant philosophy usually tended towards dogmatic realism. Euclid's geometry and Aristotle's logic were thought of as being objectively true. There was an objectively-ordered intelligible Cosmos out there, independent of the human mind and copied or mapped by our descriptions of it. Religious thought too was usually dogmatic-realist: there was an eternal world 'up there', and a created, visible world 'out there'. Only one religion reported the cosmic facts correctly, namely Christianity. Our minds, being created by God, are made to know God and can correctly track the cosmic and moral order he has pre-established for us. So, in the classic world-picture, the whole of religious truth was thought of as existing ‘out there’, independent of our minds but intelligible to us, and timeless.
After Kant we began more and more to see that all of our knowledge and our language are only human. In all our knowing, the mind conditions what it knows: the facts are profoundly shaped by the theories under which we view them and the language in which we decribe them. We are always inside our own language and our own human standpoint, and can never directly compare our vision of the world with the way the world is absolutely. We are only human. In short, we cannot claim to have purely-objective knowledge of THE world, but we can claim to have many very useful ideas about OUR world, which is the world we see and the ‘life-world’ we inhabit. For us, the only world is the human world, the world of ‘life’, and our beliefs are not pictures of the world, but tools for living.
So, very briefly: realists think that mathematical truth is discovered, whereas non-realists about maths think that maths is a complex collection of useful games invented by us. Realists think that scientists discover ‘the laws of Nature’, readymade and out there, whereas non-realists think that scientists invent theories that help us to tell stories about why things go the way they do, and to predict outcomes successfully.
Today, a realist is the sort of person who, when his ship crosses the Equator, looks overboard, expecting to see a big black line across the ocean. Realism always wishes to turn cultural fictions into objective facts. A non-realist sees the whole system of lines of latitude and longitude as a framework imposed upon the Earth by us, that helps us to define locations and to find our way around. For a realist Truth exists ready-made out there; for a non-realist we are the only makers of truth, and truth is only the current consensus amongst us. We cannot any longer suppose that our knowledge is validated by something wholly extra-human.
In brief, we don't know and we cannot know THE world, absolutely. We can know only OUR world, a world shaped by our ideas, seen from our perspective, and built by us with our needs in view. Such is Cupitt's non-realist philosophy. It implies, by the way, that we have no privileged knowledge of ourselves either, hence Cupitt's phrase "Empty radical humanism". It means "We alone improvise our knowledge about everything — including even ourselves". There is no absolute or perspectiveless vision of the world: the best we can have is a slowly-evolving human consensus about a purely human world. It doesn't sound much; but it works remarkably well in practice, which is why in America this philosophical outlook is called ‘pragmatism’.
In religion, the move to non-realism implies the recognition that all religious and ethical ideas are human, with a human history. We give up the old metaphysical and cosmological way of understanding religious belief, and translate dogma into spirituality (a spirituality is a religious lifestyle). We understand all religious doctrines in practical terms, as guiding myths to live by, in the way that Kant, Kierkegaard and Bultmannn began to map out. We abandon ideas of objective and eternal truth, and instead see all truth as a human improvisation. We should give up all ideas of a heavenly or supernatural world-beyond. Yet, despite our seeming scepticism, we insist that non-realist religion can work very well as religion, and can deliver 'eternal' happiness now.
Cupitt sees his religion of ordinary human life as the "Kingdom theology" that historic Christianity always knew it must eventually move to, after the end of the age of the Church and the arrival of a final religion of immediate commitment to this world and this life only.
This final religion, which Cupitt calls 'solar living', has a few followers everywhere, but is particularly to be found on the most liberal wing of the British Society of Friends, the Quakers. Indeed, a non-theist Friends Network UK is currently being established.