It's not just the recession that killed American employment.

And it's not just robots taking jobs from autoworkers.

The scary new dimension is artificial intelligence, which could replace as many as 50 million professional jobs according to a recent book by software entrepreneur Martin Ford. Because let's face it, Siri or something like Siri has more potential than your secretary, law clerk, radiologist or fund manager.

The Economist discusses this trend in a chilling essay. Here's an excerpt:

America's current employment woes stem from a precipitous and permanent change caused by not too little technological progress, but too much. The evidence is irrefutable that computerised automation, networks and artificial intelligence (AI)—including machine-learning, language-translation, and speech- and pattern-recognition software—are beginning to render many jobs simply obsolete.

This is unlike the job destruction and creation that has taken place continuously since the beginning of the Industrial Revolution, as machines gradually replaced the muscle-power of human labourers and horses. Today, automation is having an impact not just on routine work, but on cognitive and even creative tasks as well. A tipping point seems to have been reached, at which AI-based automation threatens to supplant the brain-power of large swathes of middle-income employees.