In linguistics, the topic (or theme) is the part of the proposition that is being talked about (predicated). Once stated, the topic is therefore "old news", i. e. the things already mentioned and understood. For example, the topic is emphasized like this in the following sentences: Linguistics is the scientific study of human language, and someone who engages in this study is called a linguist. ... In linguistics and logic, a predicate is an expression that can be true of something. ... In linguistics, a sentence is a unit of language, characterised in most languages by the presence of a finite verb. ...

• The dog bit the little girl.
• The little girl was bitten by the dog.
• It was the little girl that the dog bit.
• The little girl, the dog bit her.

The topic is also called theme, and the predicate that gives information on the topic is also called rheme.

A distinction must be made between the sentence-level topic and the discourse-level topic. Suppose we are talking about Mike's house:

Mike's house was so comfortable and warm! He really didn't want to leave, but he couldn't afford the rent, you know. And it had such a nice garden in the back!

In the example, the discourse-level topic is established in the first sentence: it is Mike's house. In the following sentence, a new "local" topic is established on the sentence level: he (Mike). But the discourse-level topic is still Mike's house, which is why the last comment does not seem out of place.

Many languages, like English, resort to different means in order to signal a new topic, such as: The English language is a West Germanic language that originates in England. ...

• Stating it explicitly as the subject (which tends to be considered more topic-like by the speakers).
• Using passive voice to transform an object into a subject (for the above reason).
• Emphasizing the topic using clefting.
• Through periphrastic constructions like "As for...", "Speaking of...", etc.
• Using left dislocation (called topic fronting or topicalization, i. e. moving the topic to the beginning of the sentence).

There are some other languages, like Japanese, that work directly on a topic-comment frame. A new topic is always introduced in a specific way, like with a topic marker (Japanese uses a postposition, wa). The topic can be the subject or the object of a verb, but it can also be an indirect object or even an oblique complement of any kind. It is always dislocated to the front of the sentence. In grammar, voice is the relationship between the action or state expressed by a verb, and its arguments (subject, object, etc. ... An object in grammar is a sentence element and part of the sentence predicate. ... A cleft sentence is a sentence formed by a main clause and a subordinate clause, which together express a meaning that could be shown using a simple sentence, but focusing on a particular constituent. ... Periphrasis, like its Latin counterpart circumlocution, is a figure of speech where the meaning of a word or phrase is indirectly expressed through several or many words. ... Dislocation is the syntaxic operation in which a constituent is detached from a phrase and taken up by a pronoun. ... A topic-prominent language is one that organizes its syntax so that sentences have a topic-comment (or theme-rheme) structure, where the topic is the thing being talked about (predicated) and the comment is what is said about the topic. ... A topic marker is a grammatical particle found in the Japanese and Korean languages used to mark the topic of a sentence. ... A postposition is a type of adposition, a grammatical particle that expresses some sort of relationship between a noun phrase (its object) and another part of the sentence; an adpositional phrase functions as an adjective or adverb. ... A topic marker is a grammatical particle found in the Japanese and Korean languages used to mark the topic of a sentence. ...

Signaling the topic as such serves the pragmatic function of avoiding repetition. In many languages, old topics are replaced with a pronoun. Pro-drop languages like Japanese tend simply to delete the old topic, which is then left implicit throughout the discourse until a new one appears. In linguistics and grammar, a pronoun is a pro-form that substitutes for a noun phrase. ... A pro-drop language (from pronoun-dropping) is a language where pronouns can be deleted when pragmatically inferable. ...

See also

• Topic marker