It may take two to tango, but one is not always the loneliest number.

Today kicks off the 23rd annual Unmarried and Single Americans Week, which aims to recognize those without spouses or significant others and celebrates their independence.  The celebration lasts until Sept. 24.

"This week is about taking an affirmative position, rather than just continuing to accept the stigma on single people as somehow defective or loners or anti-family or whatever stigmas have been placed on single people," said Thomas Coleman with Unmarried America, a nonprofit information service for unmarried people.

"It is to encourage single people to feel good about who they are and their status."

Decades beyond the era when men were expected to work and women to stay at home, the two sexes have become increasingly less dependent on one another, making living alone or living together without being married more feasible and thus more popular, according to Kei Nomaguchi, an assistant sociology professor at Northern Illinois University in DeKalb.

The 2003 U.S. Census Bureau stated that 4.6 million households consist of opposite-sex, unmarried partners, which accounts for 4.2 percent of all households, up from 2.9 percent in 1996.

Officially known by the sterile name "cohabitation," Nomaguchi said the rising trend of unmarried men and women living together stems from a controversial and non-sterile issue — premarital sex.

"Behind the acceptance of cohabitation is accepting premarital sex," she said. "Of course, parents may not be happy about it. But compared to the 1970s, people accept premarital sex more (today)."

The assistant sociology professor listed the advancement of women's rights and improvements in contraception as reasons that this contentious issue is becoming more commonplace.

Coleman differentiated between the couples who live together without plans to marry and those who use it as a trial period, deciding whether or not they can spend the rest of their lives together.

He referred to the latter as a type of reaction to the divorce rate, which boomed between the 1970s and the 1990s, splitting up many families of today's youth.

"People see what happened with divorces of family members and they don't want to repeat those mistakes, so they don't want to say 'until death do us part' until they really mean it," Coleman said.

Then there are those single people who live alone, bearing the burden as Coleman said, "of taking care of themselves completely."

This group includes a melange of people — the young, divorced, never married and widowed. And it is not always easy, according to Coleman.

The executive director of Unmarried America said single people who live alone cannot share the cost of living expenses with another person or divide household responsibilities.

He said cooking for one person is usually more difficult than cooking for two, and those who live alone are more likely to rent then own a home because the prices are too steep.

However, the number of single-person households continues to rise. The proportion of single-person households increased from 17 percent in 1970 to 26 percent in 2003, according to data from the U.S. Census Bureau.

Nomaguchi linked this trend to increasing life expectancy, leaving many older people to live alone after their spouses die, and to the rising average age of marriage.

As young people pursue higher education and focus more on their careers, the professor said they delay marriage and often times live on their own.

For Coleman, this trend of marrying later in life also highlights a positive shift in how people identify themselves. While he said in the past much of a person's self-image evolved around marriage and having children, today Coleman said people place more emphasis on personal accomplishments and their careers.

"Overall, the society is becoming more open to different family types," Nomaguchi said. "So in the 1950s, there was an ideal family — two parents and their children and they're married. But now people are becoming more and more accepting to different types of families' living arrangements."