Topic-comment relationship
A tr. should always be aware not only of the syntactic structure of the sentences he translates.
, but each simple sentence and clause consists of 2 informational segments, the theme and rheme. The theme is what a sentence is about. It’s the subject of communication. It’s a communicative reference point which has 2 functions.
1. it connects back to previous stretches of the text and in this may maintains textual coherence.
2. it acts as the point of departure by connecting forward no later stretches of the text, ensuring further textual coherence.
In the clause однако ужин по русской традиции не очень обильный, в случае приема гостей перерастает в пир. The theme is ужин. This is what the clause is about. The speaker announces the topic of his message by thematizing it.
The rheme is what the speaker says about the theme. It’s the message of the sentence. It’s the most element in the rheme fulfills the communicative purpose of the structure. The theme is the old, the  given and the known in the sentence, while the rheme is the new, unknown.
In Eng. The theme is typically expresses by the subject group and the rheme by those parts of the sentence, which are found at the end of the sentence-predicate, object.
Typical  indicators of theme in Eng.:
1.A previous reference to the idea or object in question and the use of the definite article before  the noun denoting them
2.the use of demonstrating personal pronouns before the nouns denoting the object.
Typical indicators of rheme:
1.the use of indefinite articles
2.the presence of a negatiob in the sentence
3.the construction there is/are
4.the phrases, expressing possessing to have, to own