The crucial idea in this chapter is the idea of compositionality: the syntactic structures that our mind uses to combine words play a vital role in the meaning of sentences. If a sentence has more than one grammatical tree structure, then it will be ambiguous. We also learned in this chapter that there are components of semantics that are not dependent on syntax. Linguists use thematic role labels to capture the semantic properties of participants in events, independent of the grammatical roles of the NPs. And while most languages have a typical mapping between the grammatical role of subject and the thematic role of agent, this is not the only possible mapping, and languages all have ways of overriding that mapping. Evidence from neurolinguistics suggests that syntax and semantics are processed differently in the brain, both in native speakers and in L2 learners.