The topic of a sentence is generally described as the item that the sentence is about. It is principally a notion of information structure, but it interacts in significant ways with other grammatical components, such as morphology, syntax, semantics, and phonology as well as other domains such as philosophy and psycholinguistics. Many languages have an overt, grammatical marking for topics. The nature of the marking varies greatly across languages: It can be a special morphology, a particular syntactic construction or intonation, or combination of these. As the literature reveals, it is extremely difficult to provide a formal definition for the notion of topic. First, the meaning expressed by “about” is extremely vague, being highly dependent on the discourse context, and judgements vary between speakers. Second, a difficulty arises from the fact that grammatical marking of topics is not uniform across languages. In other words, an item in a specific discourse context may be grammatically marked as a topic in one language but is not necessarily marked as such in another language. Even within one language, there is not always a one-to-one relation between a pragmatic interpretation and a linguistic marking. Finally, information structure, as an area of research, is rife with theoretical frameworks, each with its own focus and definitions. This has led to the absence of uniformity in the understanding of what a topic, among other information structural notions, is and also to there being other terminologies for the relevant item such as “theme,” “link” and “given” causing much confusion. Nonetheless, many important advances have been made toward our understanding of its properties, its role in information structure, and its interaction with the grammatical aspects of natural language. For instance, there is now a general consensus that (i) sentences are organized into different information structural units, and a topic plays a key role in its organization, along with other units such as focus (or rheme); (ii) there should be a distinction between a sentence topic, (i.e., the constituent that the sentence containing it is about) and a discourse topic (i.e., what the whole discourse is about); and (iii) there are different types of sentence topics, including aboutness topics, contrastive topics, scene-setting topics, and hanging topics, each of which is associated with a distinct set of grammatical properties. Information structure as an area of research attracted much attention in the Prague School of Linguistics, and pragmatics in the latter half of the 20th century, and since the mid-1990s, its interaction with other grammatical components has become one of the central issues in generative syntax and semantics as well as phonology and is still intensely investigated.
On the different interpretations of sentence-initial ainsi ‘so’ and the competition between three types of Verb–Subject order
