How, at the dawn of 2013, can the POSSLQ remain a form of love that has a hard time speaking its name? Forty-four percent of American adults are unmarried. Seven million Americans live with a paramour who is not a spouse. The median age of those marrying for the first time is rising. The percentage of children born out of wedlock (an atrocious term itself) is rising as well.

In his book “The Marriage-Go-Round,” Andrew Cherlin, a professor of sociology and public policy at Johns Hopkins University, details the dizzying, perhaps even nauseating, American way of marriage. We marry, unmarry and remarry again more quickly than the citizens of any other Western nation. What this means, Mr. Cherlin wrote, “is that family life in the United States involves more transitions than anywhere else.” Transitions are the hard part. Little wonder many people want to stop the marriage carousel and get off.

For many POSSLQs, being unmarried is as much a psychological state as a legal one. Joan Linder, 42, an artist and associate professor of visual studies at the University at Buffalo, lives with the man she winkingly calls her baby daddy. They have been together for seven years, share a house and a mortgage, and have two kids. “We behave a lot like a nuclear family,” Ms. Linder said. But her baby daddy — Paul Vanouse, 45, also an artist and professor in her department — is definitely not her husband, nor does she want him to be. Being unmarried makes her feel good. Ms. Linder said, “It’s the last stage of connection to rebellion, punk rock, countercultural — all those pieces of my youth.”

Mr. Vanouse feels the same. “If I’m trying to seem less weird, I’ll call Joan my wife,” he said. But he does not like the implication: that their relationship is sanctioned by the church or the state. “I would just as soon the state didn’t know I existed,” he said. “I feel the same about the heads of every religious organization.” Recently Ms. Linder and Mr. Vanouse’s older son — age 5 — came home and said, “Papa, you should call her wife!”

“He seemed to know that was kind of funny,” Mr. Vanouse said. “The way he said the word ‘wife,’ sounded so medieval.”

Sonja Lyubomirsky, professor of psychology at the University of California, Riverside, and author of “The Myths of Happiness,” suspects couples like Ms. Linder and Mr. Vanouse are onto something. Adapting to a situation tends to decrease happiness, she said, and bucking social norms tends to slow the adaptation process.