amentally the same or different has been a subject of debate for ages. This problem has deep philosophical implications: If languages are all the same, it implies a fundamental commonality-and thus the mutual intelligibility-of human thought. We are now on the verge of answering this question. Using a twenty-year-old theory proposed by the world's greatest living linguist, Noam Chomsky, researchers have found that the similarities among languages are more profound than the differences. Languages whose grammars seem completely incompatible may in fact be structurally almost identical, except for a difference in one simple rule. The discovery of these rules and how they may vary promises to yield a linguistic equivalent of the Periodic Table of the Elements: a single framework by which we can understand the fundamental structure of all human language. This is a landmark breakthrough, both within linguistics, which will thereby become a full-fledged science for the first time, and in our understanding of the human mind.