[blipmusic]

Thanks for your reply. I believe 主語 covers both subject and topic. Since an English sentence such as "John loves Mary." can be understood as e.g. "It is John (not James) who loves Mary." or "John loves Mary (not Lisa)", it might have several formal representations in Japanese via e.g. the use of wa/ga.

Also, see user gizmo686's excellent explanation for one approach below.