Conversational Interfaces, Explained

Last week at Microsoft's Build conference, CEO Satya Nadella said that the future of the company was "conversation as platform." In other words, less Windows and Office, and more Cortana and Tay--conversational interfaces that can understand the natural language of human users. If Nadella thought he was expressing some unique vision of the future, though, he was fooling himself. The idea of conversational UI has quickly colonized nearly every corner of Silicon Valley over the past year. Now seems like a good time to ask: What is a conversational interface?