In principle an ideational element is anything representing a process, a participant in a process (person, thing, institution, etc.) or a circumstance attendant on that process (time, place, manner, etc..) [...] The ideational element within the Theme, then, is some entity functioning as Subject, Complement or circumstantial Adjunct; we shall refer to this as the TOPICAL THEME, since it corresponds fairly well to the element identified as ʻtopicʼ in topic-comment analysis.
- Halliday (1985), a pag.54