To understand their arguments, it helps to understand the past.Every time a transformative invention took hold over the past two centuries â¿¿ whether the steamboat in the 1820s or the locomotive in the 1850s or the telegraph or the telephone â¿¿ businesses would disappear and workers would lose jobs. But new businesses would emerge that employed even more. The combustion engine decimated makers of horse-drawn carriages, saddles, buggy whips and other occupations that depended on the horse trade. But it also resulted in huge auto plants that employed hundreds of thousands of workers, who were paid enough to help create a prosperous middle class. "What has always been true is that technology has destroyed jobs but also always created jobs," says Nobel Prize-winning economist Joseph Stiglitz of Columbia University. "You know the old story we tell about (how) the car destroyed blacksmiths and created the auto industry." The astounding capabilities of computer technology are forcing some mainstream economists to rethink the conventional wisdom about the economic benefits of technology, however. For the first time, we are seeing machines that can think â¿¿ or something close to it. In the early 1980s, at the beginning of the personal computer age, economists thought computers would do what machines had done for two centuries â¿¿ eliminate jobs that required brawn, not brains. Low-level workers would be forced to seek training to qualify for jobs that required more skills. They'd become more productive and earn more money. The process would be the same as when mechanization replaced manual labor on the farm a century ago; workers moved to the city and got factory jobs that required higher skills but paid more. But it hasn't quite worked out that way. It turns out that computers most easily target jobs that involve routines, whatever skill level they require. And the most vulnerable of these jobs, economists have found, tend to employ midskill workers, even those held by people with college degrees â¿¿ the very jobs that support a middle-class, consumer economy.