In order to exemplify what grammatical function refers to when it comes to intonation, an example seems the best solution. Let’s take a look at the following two sentences.
Those who sold \/quickly | made a profit.
Those who \/sold | quickly made a profit.
The difference is easily seen and it is caused by the placement of the tone-unit boundary.
If you look further at the role of tone-unit boundaries and their link to units of grammar then we ca see a tendency of tone-unit boundaries to occur at boundaries between sentences, phrases, and clauses.
I won’t drink /beer | I don’t \like it. (At the boundary between sentences)
In \/Vietnam | where the density of population is \/higher | the properties tend to be more ex\pensive. (At the boundaries between phrases and clauses)
As we can see, the tone-unit boundaries are more likely to occur at boundaries between grammatical units of higher order than words.
The placement of the tone-unit boundary can indicate the grammatical structure as is shown below:
The politicians who \/like the law | are \pleased.
The poli/ticians | who \/like the law | are \pleased.
The examples clearly show the difference between “restrictive” (the first example) and “non-restrictive” (the second example) clauses. In the first example, only the politicians who like the law are pleased. The others are not pleased. In the second example, all politicians like the low therefore they are all pleased.
The choice of tone on the tonic syllable can also have a grammatical significance. For example in many varieties of English (especially American English) the rising tone is used to form questions.
The /price is going up?
The difference between falling and rising tone in question tags also create a difference in meaning.
They are leaving Vietnam on Sunday | \aren’t they?
They are leaving Vietnam on Sunday | /aren’t they?
In the first example, the speaker is sure that the information is correct, he just need confirmation. In the second example, the question tag is more like a request of information since the speaker has a lesser degree of certainty.
Many specialist in phonology said that there is an overlap between the grammatical function of intonation and the attitudinal function of intonation which may be confusing for some foreign learners of English.