This thesis focuses on the syntax of the structures with the particle le in Mandarin Chinese. The particle le has two uses: verbal le and sentential le. I will argue the verbal le in Mandarin has a dual function: it is used primarily as a quantity marker and secondarily as a perfectivity marker. This leads to a result that most of the cases with le are both telic and perfective. Others, with the lack of (im)perfectivity, only extend a quantity reading. Meanwhile, I assume the perfective reading in Mandarin solely depends on verbal le, except in negative and interrogative situations. This means in a sentence with a perfective viewpoint, even if le occurs after the object at the end of the clause, it should also be a verbal le. I argue that such a structure is result of VP-fronting. On the other hand, a real sentential le is not directly related to perfectivity. I propose that sentential le is a focus marker that scopes high in the hierarchy and yields flexible readings depending on which structure enters the focus domain under different contexts. In this sense, the configuration with both verbal and sentential le extends an assertion of a perfective event, which, I propose, functionally corresponds to the perfect aspect in English. In short, although there are two uses of the particle le in Mandarin, they should be distinguished by their grammatical functions instead of their linear positions.

This dissertation concerns one of the long-term debates about whether an innate grammar, i.e. Universal Grammar, is necessary for a child to acquire a language. The researchers who do not agree that an innate grammar needs to exist argue that the input or the child's experience of language is sufficient to acquire a language. In my work, I examine the relative clause, which is a complex structure cross-linguistically, as a case study to investigate the controversy between the role of innate grammar and the role of input in language acquisition. Based on both the comprehension data of Chinese-speaking children that I collected and the statistical analyses of corpora that I completed, I suggest that a satisfactory theory of language acquisition needs to still incorporate an innate grammar in order to accommodate the various and sometimes inconsistent input properties I document. Nevertheless, the acquisition pattern cannot be explained well without a good understanding of language-specific properties and of their potential interactions with language-external factors such as the comprehension system that may be at work in acquisition.