When you consider the challenges for the brain, it’s no wonder most of us find learning a language so demanding. We have many different memory systems, and mastering a different tongue requires all of them. There’s procedural memory – the fine programming of muscles to perfect an accent – and declarative memory, which is the ability to remember facts (at least 10,000 new words if you want to come close to native fluency, not to mention the grammar). What’s more, unless you want to sound like a stuttering robot, those words and structures have to make it to the tip of your tongue within a split second, meaning they have to be programmed in both “explicit” and “implicit” memory.