The tone-unit has a very clear internal structure and the tonic syllable is one of its components. There are two types of tone-units: simple and compound. Each simple tone-unit has only one tonic syllable.
In order to identify the head of a tone unit we are going to take a look at an example:
One-syllable utterance: \those
The same tonic syllable in a long utterance: ‘give me \those.
The head of the tone unit is the part of a tone unit from the first stressed syllable to the tonic syllable (but not including it). Notice the stress symbol before “give” and the tonic syllable “those”. If there is no stressed syllable before the tonic syllable then it means that the tone unit doesn’t have a head. In our example, “give me” is the head of the tone unit.
In the sentence ”‘Bill ‘called to ‘give me \ those”, the head of the tone unit is the first 5 syllables, from the first stressed syllable ”‘Bill” to the tonic syllable “\those”.
The pre-head of the tone unit is formed from all of the unstressed syllables that precede the first stressed syllable. There are two situations where pre-heads can be found:
The syllables that follow the tonic syllable form the tail.
\look at it
\what did you *say
\both of them were *here
Note: The symbol * represents the stress position in the tail!
We can summarize the tone unit structure as follows:
(pre-head PH) (head H) (tonic syllable TS) (tail T)