Educated and articulate, the nuns of this new generation are keen to explain their choice. Few of them see their lives as a cosy retreat, the "heaven-haven" described by Gerard Manley Hopkins. Almost all were dissatisfied with late 20th-century materialism, and have a sense of being called by a personal God. Many, having worked in therapy or counselling, have rejected these and other forms of new age soul massage.
Can the convent be seen as a good new career move, as at the end of the last millennium? In 10th-century Europe the education of girls was at worst non-existent and at best haphazard, and women were legally obliged to obey their husbands or fathers. By becoming a nun, the musician and mystic Hildegard of Bingen did indeed choose the better part. By the time she had reached her thirties she was the administrative head of a large community, and recognised by both sexes as a theological authority. She healed the sick, wrote many songs and medical textbooks, finding far more scope for her talents than she ever could have as a laywoman.
Though most modern nuns have careers before entering the convent, paradoxically their role in religion is reduced. Unlike Hildegard, they seldom get the chance to intervene in theological disputes, or go on preaching tours of monasteries and cathedrals; nor is their advice sought by bishops or heads of monastic houses. When the American theologian Madonna Kolbenschlag described today's women as "spiritual dwarves" she angered some of her readers; but arguably her description suits those modern women in religion who are denied the intellectual liberties of their medieval and renaissance predecessors.
Today's nuns are taught to see their vows of obedience as a renunciation of their own will in favour of God's. But how does God express his plans for them? Presumably not through a Pope who denies the morning-after pill to raped women in Kosovo; or who forbids feminist theologians to debate even the possibility of women priests. Church dogma is still patriarchal, and its female members are doomed for the foreseeable future to have their sacraments dispensed by men.
"Dark nights perhaps but no grey days for you," wrote Elizabeth Jennings to a friend with a vocation. Her metaphor comes from the 17th-century mystic St John of the Cross, persuaded to join the Carmelites by St Teresa of Avila. Like Hildegard a reformer, a visionary and a brilliant writer, Teresa knew how to turn boredom (grey days) into spiritual psychodrama (dark night of the soul).
But Jennings is wrong about modern nuns. Their vocations are undermined not by dark nights, but by spiritual stagnation, otherwise known as boredom. Unlike Teresa, they do not become reformers, saints, or doctors of the church. What they usually become instead is old nuns, or else quit the convent because they feel thwarted by its intellectually stifling atmosphere. Among those who stay, many are able to find confessors who condone their decision to ignore unpalatable papal dogma. But this is merely sticking plaster for wounded souls. By choosing to avoid open defiance, nuns are propping up the patriarchy that scants them.
So isn't it time that nuns redefined their role? Their God, if he exists, is presumably that same God who called Hildegard and Teresa, so he might just prize revolution over obedience. Only through a bold, confrontational engagement in theology and politics and an active support of their victimised sisters in the world will nuns regain the religious life they deserve.
Jenny Newman is the author of `Life Class' (Chatto & Windus, pounds 14.99)