Theoretical syntax is a branch of linguistics that studies the structure of sentences in a language. It focuses on how words combine to form phrases and sentences, exploring rules and principles that govern this arrangement. Theoretical syntax aims to understand the underlying systems that dictate sentence formation across different languages. Researchers in theoretical syntax often develop models to explain these structures, such as Generative Grammar proposed by Noam Chomsky. This approach seeks to identify universal principles that apply to all languages, helping linguists understand both the similarities and differences in sentence construction worldwide.