One idea is a down-to-earth belief that one must work at keeping love alive through compromise, personal growth or religious faith. The other is a Hollywood movie, romantic belief in the existence of one everlasting "true" love, said Ann Swidler, author of a study of American middle class cultures of love.

Swidler discovered that people shift back and forth between these two belief systems, stitching together an explanation for their choices in love and marriage.

"We believe in a love that is totally committed and totally chosen," said Swidler. "Our belief in love goes very deep, precisely because it is contradictory and binds two opposing ideas."

Her analysis of interviews with 88 married and divorced middle class Americans from the suburbs of San Jose, Calif., is published this month in a new book, "Talk of Love: How Culture Matters" (University of Chicago Press).

"Two cultures of love persist, neither driving out the other, because people need both and employ them in very different situations," said Swidler.

Not everyone, however, readily admits to having the romantic belief. In fact, most of her interviewees said that love had to be created on a daily basis through work, and that it didn't come automatically. Many were critical of romantic "myths," insisting that they are dangerously misleading, said Swidler.

Nevertheless, Swidler said, time and again at critical points in the interviews, the romantic belief "would erupt, in the conversation of people who thought they didn't believe in it."

This belief surfaced when interviewees talked about whether they would stay in their marriages no matter how difficult the marriage might become, through illness or other kinds of adversity, she explained.

"They would say, 'If you love that person, you will stay no matter what.' And if you leave, that means it wasn't 'real' love," said Swidler.

The belief in one true love provides the underpinning for a permanent commitment in marriage - an institution that has become totally voluntary and is no longer supported by effective social or legal sanctions, said Swidler.

"People have to constantly remake the decision to stay married," said Swidler. "This is the 'free choice' part of the paradox, which is answered by belief in a mythic love where choice is absolute and enduring, because there is only one person in the world for you."

She said that ideas of love are becoming ever more multifaceted as the institution of marriage becomes more complex and uncertain. People draw on different images of love depending on the life challenges they face.

"Romantic love exists to get people into and out of marriage," says Swidler. "If you are truly not contemplating marriage, you can dispense with the idea. But if you are making a decision about commitment, you are likely to rediscover the idea of 'one true love.'"

She referred to one man whose wife left him to marry his best friend. Totally disillusioned, he thoroughly rejected the idea of love, preferring to talk about friendships and relationships. He stopped thinking there was any one "right" person and began to think "you could take seven, eight, nine or ten of these people (his dates) and you could marry any one of them and have a good marriage."

Then, when he found a new woman he wanted to marry, he retrieved the idea of one true love, saying such things as, " She was different from all the rest. She was just so perfect!"

In contrast to the idea of true love, Swidler said that people often use the word "love" when they speak of their feelings for friends, but they never ask "Is this 'real' love? Is this it?" because there is no all or nothing decision that has to be made about friendship.

"You wouldn't ask that question unless you had the institution of marriage looming over you. To form a marriage, you must get to the point of deciding that one other person is 'it,'" she said. " But to maintain the marriage, you need the more realistic-prosaic belief that love is created on a daily basis."