A classic problem in linguistics is explaining how learners come to know so much about their native languages, despite receiving limited and noisy input. This learning problem becomes especially acute when the linguistic properties in question are obscure and show subtle variation across languages. Cross-linguistic variation means that learners must identify the appropriate points of variation for their language, even though the direct evidence that they need is often hard to detect or even non-existent.
This dissertation presents two case studies on constraints in A-bar movement. Because constraints are by nature abstract and difficult to observe directly, a classic solution to the learning problem posed by constraints claims that knowledge of these abstract or negative linguistic properties is innate. However, a number of these constraints show cross-linguistic variation, raising questions about how they are represented and how linguistic experience might (or might not) shape linguistic knowledge.
The first case study, discussed in chapters 2 and 3, involves cross-linguistic variation in the constraint that governs A-bar movement from relative clauses: some, but not all, languages allow A-bar movement from relative clauses under exceptional circumstances. I argue that these 'porous' relative clauses that permit A-bar movement can be distinguished by a property that I call 'tense dependence,' and discuss how this tense property might be formally related to A-bar movement. I show that this particular kind of variation presents a learning problem: in languages like English and Mandarin Chinese, learners have little direct positive evidence that such A-bar movement is possible. Using tense dependence, I propose that learners might circumvent this absence of direct evidence by relying on A-bar movement from a superficially unrelated structure: non-nite purposive clauses. The second case study, discussed in chapter 4, involves bridge verbs: within a given language, some verbs allow A-bar movement and others do not; in addition, the set of verbs that allow A-bar movement varies across languages. I present an acceptability judgment experiment that is aimed at clarifying existing generalizations about bridge verbs in English. With more secure generalizations in hand, I discuss the extent to which bridge effects have a pragmatic origin, bringing in data from an informal survey of English and Dutch native speakers that looks at the effect of context on long-distance A-bar movement. Echoing existing work, the survey shows what appears to be a case of cross-linguistic variation between English and some Dutch varieties for cognitive factive verbs. To account for this instance of cross-linguistic variation, I suggest that English learners might have limited access to direct evidence, and discuss what learning mechanisms a learner might need to draw the language-appropriate conclusions based on sparse evidence.
Chapter 5 discusses the consequences these case studies have for our formal accounts of these constraints. I evaluate existing proposals and argue that the range of variation observed requires more flexibility than what many existing proposals can offer
Chapter 6 concludes.