In 1995, Sherry Turkle, a professor of the “social studies of science” at M.I.T., published a book about identity in the digital age called “Life on the Screen.” It was a mostly optimistic account, as Turkle celebrated the freedom of online identity. Instead of being constrained by the responsibilities of real life, Turkle argued, people were using the Web to experiment, trying on personalities like pieces of clothing. As one online user told her, “You are who you pretend to be.”

In Turkle’s latest book, “Alone Together,” this optimism is long gone. If the Internet of 1995 was a postmodern playhouse, allowing individuals to engage in unbridled expression, Turkle describes it today as a corporate trap, a ball and chain that keeps us tethered to the tiny screens of our cellphones, tapping out trite messages to stay in touch. She summarizes her new view of things with typical eloquence: “We expect more from technology and less from each other.”

“Alone Together” is really two separate books. The first half is about social robots, those sci-fi androids that promise (one day) to sweep the kitchen floor, take care of our aging parents and provide us with reliable companionship. As always, though, she’s less interested in the machines than in our relationships with them. Turkle begins with the troubling observation that we often seek out robots as a solution to our own imperfections, as an easy substitute for the difficulty of dealing with others.

Just look at Roxxxy, a $3,000 talking sex robot that comes preloaded with six different girlfriend personalities, from Frigid Farrah to Young Yoko. On the one hand, it’s hard to argue with the kind of desperate loneliness that would lead someone to buy a life-size plastic gadget with three “inputs.” And yet, as Turkle argues, Roxxxy is emblematic of a larger danger, in which the prevalence of robots makes us unwilling to put in the work required by real human relationships. “Dependence on a robot presents itself as risk free,” Turkle writes. “But when one becomes accustomed to ‘companionship’ without demands, life with people may seem overwhelming.” A blind date can be a fraught proposition when there’s a robot at home that knows exactly what we need. And all she needs is a power outlet.