Syntax is the study of the structure of sentences, the principles, both universal and language specific, that govern how words are assembled to yield grammatical sentences.

At Penn, most syntactic research focusses on syntactic variation, across languages and over time. 

Julie Anne Legate combines state-of-the-art linguistic theory within the Minimalist framework with detailed study of languages across the globe.  A main theme of her work is to describe the richness of variation found in lesser-studied languages, and to demonstrate the deep, structural similarities between these languages and more familiar languages. This approach has allowed her to address fundamental questions in syntactic theory concerning the basic organizing principles of syntax, cyclic domains in sentence structure, the grammatical function “subject”, case and thematic relations, and voice alternations. 

Corpus linguistics has been a focus at Penn ever since Mitch Marcus and others created the first syntactically parsed corpus of English, the Penn Treebank in 1992. Since then, Anthony Kroch and Beatrice Santorini have participated in the development of historical corpora of English, resulting in the Penn- Helsinki Parsed Corpus of Middle English and the Penn-Helsinki Parsed Corpus of Early Modern English. These have been instrumental in learning about syntactic changes that have occurred over the past millennium, such as the loss of verb-second syntax in English, and for the understanding of grammar competition, advocated by Anthony Kroch.

David Embick has been investigating the syntax-morphology interface primarily under the framework of Distributed Morphology, which claims that the same combinatory framework at work at the level of syntax applies down to the level of the morpheme as well. Such an approach has been useful for reframing the notion of blocking at the level of syntactic constituents, as well as understanding mismatches between surface and structural positions of morphemes.

At Penn, syntax may also be investigated through the mathematically defined formalism known as Tree Adjoining Grammar (TAG), lead by TAG's creator, Aravind Joshi, and Anthony Kroch. Current research in TAG focuses on new extensions of TAG called Multi-Component TAG, the creation of a metagrammar for wide-coverage grammars of natural languages, and the formal properties of the new extensions to TAG. 

Robin Clark, who now is focusing on game-theoretic approaches to semantics, completes the picture of syntax offered above by introducing his students to Categorial Grammar, an important alternative approach to syntax advanced by former Penn professor Mark Steedman.