The nucleus is the tonic syllable of a sentence. It contributes to the meaning to such utterances of speaker. Enunciatively (the way the speaker utters), it's the main part of the opinion's talker.
A sentence has usually a word that stresses the importance or the interest of which the speaker wants to let the hearer know its intention or say.
There can be different aims at what the speaker refers to:
- Place: I'm going to 'Oxford.(Where are you going )
- Subject:'I'm going to Oxford (Is anyone going to Oxford)
- targeted verb:I'm 'going to Oxford ( What are you doing for your training course)
Of course there may be other intentional indications that the speaker gives to the hearer focusing on its communicative devices.