English evidential -ly adverbs from a functional perspective

Every language has ways of expressing evidentiality, in other words, ways of expressing the provenance of information. English has a number of -ly adverbs that do just that. The most frequent of these adverbs are analysed in this book: reportedly, purportedly, allegedly, supposedly, evidently, presumably, seemingly, apparently, obviously, clearly, visibly. Examples of these adverbs in use in recent UK English newspapers have been extracted from the NOW corpus.
The adverbs were categorised into four different evidential categories of Functional Discourse Grammar (FDG), which is a structural-functional approach with a layered hierarchy. According to their meaning, the adverbs are categorized into the four evidential subcategories recognized in FDG: the reportative, inferential, deductive and event perception. By applying tests using FDG layers, the behaviour and distribution of the evidential subcategories of evidential -ly adverbs are determined. The focus is on their occurrence and constraints on the use of these adverbs in main clauses, clausal complements and noun phrases.
The results show that some adverbs belong to more than one evidential subcategory and thus belong to more than one FDG layer. These evidential adverbs are viewed as
chameleon-like as their meaning is determined by the local context in which they occur.
Furthermore, it has appeared that FDG is a theory that can be applied to reveal more about the meaning of English evidential -ly adverbs. Although English evidential adverbs belong to different FDG layers with different meanings, they all serve to mark a knowledge base as source of information.