Universal Grammar (UG) refers to the innate linguistic principles that are shared across all human languages. While UG plays a significant role in first language acquisition, its role in second language acquisition is more limited according to several theories. Native language has a major influence on second language acquisition, and there are fundamental differences between how children and adults acquire language as outlined in Bley-Vorman's Fundamental Difference Hypothesis. UG may influence second language acquisition indirectly through the influence of native language grammar rather than acting directly on the learning process.