Sister Lavinia Byrne, a prominent Catholic sister and regular contributor to Radio 4's Thought For The Day, says temporary vows would encourage more women to adopt a religious life.
The number of women in religious communities in Britain has dropped from more than 11,000 a decade ago to just over 9,000 today. And only 20 women took up convent life in Ireland last year, compared with 100 a decade ago, according to the Religious Vocation Association. Fewer than 10 are expected to take final vows in the next year.
Religious organisations blame the decline on the emancipation of women. In the past, young girls had to join convents to serve God, whereas today they have numerous options, including voluntary work abroad.
"It's not that girls are no longer religious," said Sister Lavinia, who belongs to the Institute of The Blessed Virgin Mary. "It's just that women have other choices which they never had before. The church needs to realise that people find it hard to make lifelong commitments and allow women to take their vows for a temporary time."
However, Sister Lavinia says there has been a renaissance in the number of women choosing to join contemplative orders. These women, the only sisters who can accurately be referred to as nuns, live apart from the community, unlike religious sisters who are members of apostolic orders and work outside, often as teachers or nurses.
"I think the contemplative life offers an attractive alternative to the hurly burly of modern life," said Sister Lavinia. "There has been a huge increase in people going to retreats in this country. If joining a religious community forms a temporary part of a person's overall religious experience then that should be accepted."
A lifetime commitment to God was the only religious path available to Sister Madeleine Simon, when she became a religious sister 66 years ago. Now 86, she belongs to the apostolic Society of the Sacred Heart and has devoted her life to teaching and to prayer. Home is a house in Roehampton, Surrey, with 20 other sisters.
"I came from a well-to-do family who were strongly Roman Catholic and in those days that meant you either got married or stayed at home looking after your parents'" she said. "Or you followed God.
"In my day you entered at 17 and never knew a different world. Now all religious orders prefer you to be older and really know what you are doing. There are many people who are prepared to commit to something for a year, but this is a commitment for life - that's hard."
Life for Sister Teresa Ryden, 34, does not differ radically from that of her secular contemporaries. She takes the Tube to work in the accounts department of a charity. In the evening she often visits the cinema after prayers with the three other sisters with whom she shares a house in Hammersmith, west London.
"I did have other options in following God but I felt becoming a sister was the best way for me," she said. "By taking a vow of chastity you have the freedom to devote your time and affections to God and others who need you.
"However, there is no such thing as a job or a relationship for life these days and it's not surprising that many people find it off-the-wall thinking about a permanent commitment. When I took my vows I was taking them with the best intentions - but I cannot predict the future."
Carmelites (contemplative): Founded in the 12th century. Devote much time to divine service and meditation. Lead strict life with severe fasting.
Poor Clares (contemplative): Follow rules of Clare of Assisi, who died in 1253: strict fasting; may possess no property.
Benedictines (contemplative): No involvement in outside world, apart from shop or hospital. Talk limited to necessary topics.
Dominicans (apostolic/ contemplative): Concentrate on study, teaching and preaching.
Augustinian (apostolic): Nursing and teaching.
Ursulines (apostolic): Founded 1535; carry out charitable work and religious instruction.Reuse content