Topic and Comment

The topic-comment structure is a fundamental mechanism of Bantu information structure, used in all registers of Swahili from casual conversation to formal news broadcasts.

Why use it?
It is often used instead of the passive voice when you want to give prominence to the object but maintain the active voice and the original subject. For example, instead of saying "The book was read by me" (passive), it is often more natural to say "The book, I read it" (topic-comment).

The Mandatory Object Marker
In standard Subject-Verb-Object sentences, the object marker is obligatory for animates but depends on definiteness for inanimates. However, in the topic-comment structure, it is strictly obligatory for both. When an inanimate object is fronted as a topic, its corresponding object marker becomes strictly obligatory to link the comment back to the topic.

Compare:

• Nilikisoma kitabu. (Standard SVO with object marker for definiteness)
• Kitabu, nilikisoma. (Topic-comment: The book is fronted, comma indicates a pause, object marker -ki- is mandatory)

Topic vs. Contrastive Focus
It is crucial to distinguish between fronting an object as a topic and emphasizing it for contrastive focus. If you are emphasizing what the object is in contrast to something else (e.g., "It is a BOOK that I read, not a newspaper"), you do not simply front it. Instead, you either leave it in its normal position with vocal emphasis, or use a cleft construction. Note that the Topic-Comment structure uses the Object Marker (like -ki-), whereas the Cleft construction requires a relative clause, thus using the Relative Marker (like -cho-). While clefts require the Relative Marker, formal object clefts normally include the matching Object Marker as well as the Relative Marker (e.g., Ni kitabu nilichokisoma.). Additionally, keep in mind that internal relative markers cannot be used with certain tenses (like the perfect tense -me-), requiring the amba- relative instead.

• Kitabu, nilikisoma. (Topic: As for the book, I read it. -> OM -ki- required)
• Nilisoma KITABU. (In-situ Focus: I read a BOOK.)
• Ni kitabu nilichosoma. (Cleft Focus: It is a book that I read. -> RM -cho- required)

Additional Mechanics

• Explicit Subjects: If you use an explicit subject, it can be placed before or after the fronted topic (e.g., Mimi, kitabu nilikisoma or Kitabu, mimi nilikisoma).
• Dropping the Topic: Once the topic is established in context, the fronted noun can be dropped entirely. The mandatory object marker remains to carry the reference (e.g., Nilikisoma. = "I read it.").
• Right Dislocation (Afterthoughts): This exact same rule applies if the topic is moved to the end of the sentence as a clarification or afterthought (e.g., Nilikisoma, kitabu. = "I read it, the book."). The object marker remains strictly mandatory.

Relative Shape and Future:
The bound future relative uses -taka-, as in kitabu nitakachokisoma (the book that I will read), not ordinary -ta- with an appended relative. A Class 7 object marker is -ki-, while its relative marker is -cho-; similarly Class 8 has -vi- and -vyo-. Keep these separate concord series distinct.