Tonic Syllable

 In English intonation, the tonic syllable is the most important part of any sentence (or unit of speech). The intonation pattern for the unit begins on the tonic syllable, and it is the place with the strongest stress. In the following examples, the tonic syllable is underlined:

Have you ever been to Cuba?
It’s wonderful!
Why are you so happy about it?
They told me!

As the examples show, the most likely place for the tonic syllable is in the last content word (verb, noun, adverb etc.) in a unit.

This will always be dictated by the meaning of the sentence, however, so a more general rule is to place the tonic syllable in the last important word in a unit, and this is dictated by the meaning in context, compare:

Why are you going?
Why are you going?

The tonic syllable is unlikely to appear on a function word (auxiliary verb, preposition, conjunction etc) except to produce a specific meaning like in the example above (I know where he is going, now I need to know where you are going) with a focus on the pronoun you.

A unit of speech has one tonic syllable and one intonation pattern.