Whether all human languages are fundamentally 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. Using a theory that is over 20 years old, proposed by 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 breakthrough, both within linguistics, which will thereby become a full-fledged science for the first time, and in our understanding of the human mind.