This document discusses the concepts of theme and rheme and how they help understand how information is conveyed in clauses. Theme refers to the element that serves as the starting point of the message in the clause, while rheme is the remainder of the message. Themes can be unmarked or marked. Unmarked themes are typically nominal groups, while marked themes involve other elements like complements. Clauses also contain elements like subjects, verbs, complements, and adjuncts. Themes can be simple, consisting of just one constituent, or multiple, containing different types of themes.