Brazilian Portuguese is a language that makes prolific use of word-order permutations to indicate Information Structure processes (topicalization and focalization); in particular, two main areas of the clause (left periphery and middle field) can host dislocated elements with non-neutral interpretation in discourse. This dissertation aims to contribute to the understanding of the Syntax-Information Structure interface in natural languages by investigating the syntactic and informational properties of elements displaced to the middle field of Brazilian Portuguese, through a systematic comparison with its left periphery. I investigate the conditions regulating the distribution of different types of topics and foci, aiming to shed light on the question of how syntactic structures are mapped onto the Information Structure component of the grammar.
The investigation reveals a number of asymmetries between the left periphery and the middle field; most notably, the informational roles available in the latter are a proper subset of those available in the former. This observation allows us to address a number of factors that play a role in the licensing of different topics and foci in the language. I also show that the same structural position can license more than one informational role and that the same informational role can be licensed in more than one structural position (e.g., aboutness topic interpretation is possible in both the subject position and a left-peripheral topic position). Based on that observation, I argue for a contextual approach to Information Structure, where topics and foci are not tied to structurally-fixed positions in the clause, but are instead contextually licensed based on their relative position with respect to each other and other information-structure elements.
In doing so, I analyze the structural make-up of the middle field of Brazilian Portuguese. I argue that the language has (formally-driven) object shift to an independent projection above vP, to which middle-field topics adjoin. The comparison of syntactic and interpretive properties of shifted objects and middle-field topics is shown to have a number of consequences for different theoretical issues, including labeling and locality/phases, and provides evidence for the status of Information Structure as an independent component of the grammar.