THE QUAKERS are well-known as the least doctrinaire of all the religious movements that have emerged from Christianity.

Silent reflection has been the hallmark of their gatherings ever since 1652 when George Fox, an independent-minded preacher, had a hill-top vision in the English Lake District which convinced him that many people would adhere to his free-ranging form of faith. All people, he believed, have God inside them and can experience the divine without mediation by clerics. With an influence on world affairs that far outstrips their numbers (below 500,000), the Quakers have won respect for their willingness to undertake a quest for truth whose end-point cannot be prejudged.

In the developing world, especially Africa and Latin America, the Quakers have come to look more like other Christian denominations, with pastors and set services. But in the movement’s British heartland and elsewhere in the northern hemisphere, it is increasingly open-minded on the ultimate religious question: whether or not there is a God.

Perhaps this is not so surprising. An avoidance of universal axioms is a deep-rooted instinct among members of the Religious Society of Friends (the movement’s formal name). They generally share a commitment to social justice, peace and equality but have often differed (sometimes politely, sometimes not) about other things. Their history is peppered with open splits, not only over metaphysics but over earthly issues that had big consequences. Pennsylvania’s emergence as a cradle of American democracy and freedom of thought owed much to the initially lofty, Quaker-inspired ideals of the Penn family who founded the place; then radical Quakers became the Penns’ strongest critics, callling them greedy and provocative to the Indians. Some early American Quakers had slaves; after the Revolution followers of the faith became passionate abolitionists.

Pinning down what Quakers actually believe about anything is a “very difficult question”, according to Ben Pink Dandelion, who runs a Quaker studies centre at the University of Birmingham. Recently it has become harder still because the movement has attracted so many people who like its values and ethos but do not hold typically Christian beliefs.

They include a growing number of “non-theists”. Fully 43% of Quakers in Britain do not profess a belief in God. There is a contingent who positively deny the existence of God: they now account for 14.5% of British Quakers, up from just 3% in 1990, according to research by Jennifer May Hampton of Cardiff University. As well as firm God-deniers, the non-theists include agnostics and those who believe in an undefined spiritual force.

David Boulton, a broadcaster and author, is among those who think there is no transcendent God and is even “a bit queasy about the word spiritual”, preferring to call himself a humanist. But he feels comfortable as a Quaker. By contrast Nat Case, a cartographer and non-theist Quaker from Minneapolis, is more open to talk of the supernatural, though he rejects the idea of an external God. He compares his relationship with religion to his appreciation of “Star Wars”: “You don’t need to know the lines from all the movies…It’s about how it grabs you.”

Ms Hampton’s research found that Quakers who eschew conventional belief in God and the Bible are also less committed to the core Quaker doctrine of pacifism in all circumstances. Neither she nor other researchers can be sure why. Hitherto the non-theists have also been less likely to hold positions of responsibility within the Society, or to participate in the collaborative decision-making process whose stated aim is to discern the will of God.

Atheist Quakers tend to be quite firm in their lack of belief, whereas Quakers who call themselves theists are often contentedly uncertain about the nature of God’s existence or character, as is noted by Mr Dandelion. He says his own personal beliefs are quite typical of Quakerism. He has the strong sense of a personal relationship with a divine presence, to which he turns for guidance, even on mundane matters. But he is reluctant to speak of God’s characteristics. “I can’t describe God, but there is something,” he says. He describes the term God as “a shorthand for the mystery”.

The Quaker movement’s retreat from conventional theism goes back at least to the 1930s, when members started placing less emphasis on the Bible as a guide to spiritual experience. That trend accelerated after the second world war, and in 2011, a Non-Theist Friends Network was established. At first this seemed to portend an open split, but this fear has apparently receded. At last month’s annual gathering of the network there was much eirenic talk of diversity and unity.

Now the Quakers are updating their terminology. Reports that the word “God” could be dropped from the revised guidelines ruffled feathers when they emerged last year. Theists and non-theists alike insist this is not the case, but, as Mr Dandelion points out, secular language is increasingly being used to describe what were previously thought of as spiritual processes.

For instance, “God in everyone”, a traditional Quaker phrase, is often replaced by the expression “good in everyone”. Some Friends now talk of “discerning the sense of the meeting”, rather than “the will of God” during worship and decision-making. If that change is promoted aggressively, it may in time lead to a schism. One Quaker describes pushes by atheists to change the movement’s language as “a bit like joining a swimming club and saying: ‘We don’t like water, why don’t we change it into a walking club.’”

On the other hand, there is less obvious need for the movement’s original function, which was to provide an alternative to overbearing, bullying established churches backed up by the armed authority of states. Shedding some religious nomenclature might bolster Quakerism’s attractiveness both to community-seeking atheists and spiritual agnostics. The question is how amorphous a movement can become with disappearing into thin air.