Dynamic focus
Focus is not static but dynamic. As the conversation progresses, speakers constantly update what they are focusing on. Consider a simple example. The family are sitting in a room at the back of the house when the doorbell rings. Dad says to his son:
'Vernon, | there's ▸someone at the 'door. | 'Answer it, would you?
The boy does so and come back to report:
There's 'man at the door. He's ▸collecting for 'charity
In the father's utterance, door was new information, and therefore placed in focus. In the son's reply, it is given, and so no longer in focus.
By varying the tonicity (= changing the accent pattern, altering the focus, putting the nucleus in different places) we make a particular IP pragmatically appropriate for particular circumstances in which it is used. The most obvious reason for doing this is to express different kinds of contrastive focus.
Consider the utterance she was trying to lose weight. With broad focus, and therefore neutral tonicity, it would be said as:
She was ▸trying to lose 'weight
This might in broad-focus answer to:
〉 Why didn't she want an ice cream?
》 She was ▸trying to lose 'weight.
But we would have the same tonicity in a narrow-focus answer to:
》 She was ▸trying to lose 'weight.
〉 What was she trying to lose?
》 She was ▸trying to lose 'weight.
... or in contrastive-focus follow-on to:
》 She was ▸trying to lose 'weight.
She ▸wasn't trying to loose 'money, | she was ▸trying to lose 'weight
What about focusing on some other element in the utterance? If we put contrastive focus on lose, we imply a contrast between lose and some other item:
She ▸wasn't trying to 'gain weight, | she was trying to 'lose weight
With contrastive focus on trying:
She was 'trying to lose weight | thought she 'didn't have much suc'cess
With contrastive focus on was the contrast must either one of tense one of polarity
She 'was trying to lose weight, | but she ▸isn't 'now
She 'was trying to lose weight, | de▸spite your claim that she 'wasn't
Contrastive on she implies a contrast with some other possible subject:
She 'was trying to lose weight, | de▸spite your claim that she 'wasn't
'She was trying to lose weight, though her 'friends may not have been
In lively conversation speakers constantly deploy contrastive focus, shifting the place of nucleus around appropriately. Always keeping the nucleus on the last new lexical item can sound very dull.