When French literature and history scholar Joan DeJean set out to understand the story behind comfort, she started by looking at the history of the sofa.

Today, this piece of furniture is ubiquitous in homes, but prior to its innovation in the late 1680s in France, no such piece existed. People sat on hard, straight-backed chairs (though that changed around this time, too), or on trunks. Padded seating was an utterly unrealized concept.

In her latest book, “The Age of Comfort,” DeJean, the Trustee Professor of Romance Languages in the School of Arts and Sciences, says the sofa set off a design revolution, being the first piece of furniture that featured upholstery and padding on all sides. This new seat encapsulated a move toward comfort that began in France around 1670, and lasted until 1765.

In that relatively short period of time, many of the things that we still associate with comfortable living—private bedrooms and baths, loose-fitting cotton clothing, indoor toilets and padded furniture—came into being and flourished. In ways both big and small, these ideas about comfort forever changed the way people lived. DeJean writes, “The age of comfort can be said to have created a blueprint for today’s home and the way we live in it.”

For her book, DeJean explored architectural treatises from the 18th century, and worked with collectors at London’s Victoria and Albert Museum to see what could be learned from the intersection between period texts and objects. DeJean also read real estate advertisements, which began to appear around the mid-18th century, and looked closely at Versailles palace life, as well as at people of more modest means who embraced the aesthetics of comfort, such as the actress Charlotte Desmares.

Not surprisingly, the first to embrace this way of life were the rich and powerful who called Versailles home. While “Sun King” Louis XIV created what DeJean says was “the greatest court culture that Europe had ever seen” at Versailles, it was his son and successor, Louis XV, who instilled many familiar forms of comfort. He ripped open the palace’s massive walls numerous times, beginning in 1728, in order to install indoor plumbing. He also was the first to assert that he had the right to live part of his life out of the public eye. Until that point, casual living out of the spotlight was out of the question for royals and the elite.

“Privacy is redefined during every period,” says DeJean. “This was a period when new lines were being drawn to remove things from the public eye.” For the first time, she says, the elite created rooms dedicated to washing and the toilet, and reserved the bedroom for sleeping.

The creation of these new comfort rooms begged for new ways to fill them, and DeJean writes that the 18th century is often referred to as the golden age of furniture design. In the 1660s, before comfort became the norm, DeJean says almost no seating existed in bourgeois homes.

“People sat on beds, which were moved into the main room to be near the fire. People sat on the bed and a couple of stiff, wooden chairs,” she says. “A century later, in bourgeois Paris, [houses had] a separate bedroom, and there were chimneys in all rooms. ... People had furniture and armchairs upholstered.” Storage changed as well, with trunks being abandoned in favor of chests of drawers and closets.

DeJean notes that devotees to comfortable living took the padded furniture as an invitation to lounge—an attitude that was furthered by the introduction of looser, lighter fabrics from the east. “The introduction of cotton changes things immediately,” says DeJean of the washable, lighter fabric.

But loose clothing made some worry.

“People objected to many things,” she notes. “They objected to the way women dressed, they objected to the sofa, which was a sexy piece of furniture. People objected to the new kinds of behavior.”

France didn’t have a lock on comfort forever, and by the late 1750s and 1760s, the country’s role as dominant tastemaker was beginning to wane. When the French Revolution began in 1789, certain aspects of the comfortable life quickly became things of the past. The most luxurious homes were gutted and opened to the public, and most of the metal pipes were ripped out of buildings during the Revolution and Napoleonic era to contribute to the war effort.

DeJean notes that dress design also shifted during the 19th century to more confining garments. “In dress and furniture and body language, there are just trends,” she says. “One generation will become very casual, and the next will want formality as a response. The things that we consider more essential and life-changing, those things continue.”