Every once in a while nature gives us insight into the human condition by providing us with a unique case whose special properties illuminate the species as a whole. Christopher is such an example. Despite disabilities which mean that everyday tasks are burdensome chores, Christopher is a linguistic wonder who can read, write, speak, understand and translate more than twenty languages. On some tests he shows a severely low IQ, hinting at ineducability, yet his English language ability indicates an IQ in excess of 120 (a level more than sufficient to enter university). Christopher is a savant, someone with an island of startling talent in a sea of inability. This book documents his learning of British Sign Language, casting light on the modularity of cognition, the modality neutrality of the language faculty, the structure of memory, the grammar of signed language and the nature of the human mind.