How machines learned to speak human language

THIS past Christmas, millions of people will have opened boxes containing gadgets with a rapidly improving ability to use human language. Amazon's Echo device, featuring a digital assistant called Alexa, is now present in over 5m homes. The Echo is a cylindrical desktop computer with no interface apart from voice. Ask Alexa for the weather, to play music, to order a taxi, to tell you about your commute or to tell a corny joke, and she will comply. The voice-driven digital assistants from America's computer giants (Google Assistant, Microsoft's Cortana and Apple's Siri) have also vastly improved.