Cogito, ergo sum. We’ve all heard that famous assertion, foundation for a modern philosophy of self, consciousness, and individualism. But Descartes had it easy: for him, thought was self-evident — he didn’t have to define it. What is thought? What is intelligence? And can a machine be said to possess either? The field of artificial intelligence, it turns out, is as much about the questions as it is about the answers, and as much about how we think as whether the machine does.