Lexical and Syntactic Rules in a Tree Adjoining Grammar

according to this definition 2. Each elementary tree is constrained to have at least one terminal at its frontier which serves as 'head' (or 'anchor'). Sentences of a Tag language are derived from the composition of an S-rooted initial tree with other elementary trees by two operations: substitution (the same operation used by context free grammars) or adjunction, which is more powerful. Taking examples from English and French idioms, this paper shows that not only constituent structures rules but also most syntactic rules (such as topicalization, wh-question, pronominalization ...) are subject to lexical constraints (on top of syntactic, and possibly semantic, ones). We show that such puzzling phenomena are naturally handled in a 'lexJcalized' formalism such as Tree Adjoining Grammar. The extended domain of locality of TAGs also allows one to 'lexicalize' syntactic rules while defining them at the level of constituent structures.