The study focuses on manner adverbials and the structure of Finnish sentences, addressing the following questions: why do Finnish manner adverbials have so many different forms, and where does the manner meaning come from? How are manner adverbials licensed, and what is their original position of merge? Why do obligatory and optional manner adverbials have exactly the same distribution? Why do they behave in the same way in linguistic operations such as movement? Finally, why is the relative ordering of Finnish sentence-final manner, place and time adverbials not fixed? In the thesis, I develop a system of grammatical and semantic case which allows us to analyse all manner adverbials as KPs with semantic case. I also show how the system of case can be integrated into the linear correspondence Axions of Kayne (1994) and the minimalist programme of Chomsky (1995). I then develop a system of phrase structure in which the UP is divided into domains, and show that arguments within a single domain are not hierarchically ordered with regard to each other.