Chapter 1. What is easy and what is hard to acquire 
in a second language

Explaining why some linguistic features and constructions are easy or difficult to acquire in a second language has become a prominent current concern in generative second language acquisition (SLA) research. Based on a comparison of findings on the L2 acquisition of functional morphology, syntax, the syntax-semantics and syntax-discourse interfaces, the Bottleneck Hypothesis argues that functional morphemes and their features are the bottleneck of L2 acquisition; acquisition of syntax and semantics (and maybe even the syntax-discourse interface) flows smoothly (Slabakova 2006, 2008). The chapter presents recent experimental studies supporting this view. A pedagogical implication of this model is discussed, namely, that an enhanced focus on practicing grammar in language classrooms is beneficial to learners.