Universal grammar is a theory in linguistics proposed by Noam Chomsky, suggesting that all human languages share a common underlying structure. This idea posits that the ability to acquire language is innate to humans, meaning that children are born with an inherent understanding of grammatical principles, regardless of the specific language they are exposed to. According to this theory, the differences among languages arise from variations in surface structures, while the deep structures remain consistent across cultures. Universal grammar aims to explain why children can learn complex languages quickly and efficiently, highlighting the cognitive mechanisms that facilitate language acquisition.