Sentence:  The obvious question to ask at this point is: ‘Why posit the existence of a set of Thematic Relations (<small>THEME</small>, <small>AGENT</small>, <small>INSTRUMENT</small>, etc.) distinct from constituent structure relations?ʼ The answer given in the relevant <WSD>literature</WSD> is that a variety of linguistic phenomena can be accounted for in a more principled way in terms of Thematic Functions than in terms of constituent structure relations. 
Meaning of the word marked with <WSD> tags:  All the papers, treatises(,) etc. published in academic journals on a particular subject.