Are there hidden rules for English intonation?
For multi-syllable words, I found native speakers often use an intonation different from the dictionary.
for example, the word "lesson", they usually lower the tone of the first syllable "le", and raise the tone of the second syllable "son"
Why is it like that? Is there any hidden rule for this which is unknown or not explained to non-native speakers?
Dictionaries don't indicate tone but stress, which in English is not only determined by tone (like in Japanese) but also by other factors like the length and loudness of a syllable.
In the sample you linked to, "slightly" is in fact pronounced with the stress on the first syllable, just as the dictionaries say, even though the second syllable has a higher tone.
Lowering the tone in the first syllable is just meant to make the reading sound less monotonous. Talking like that in casual speech might even sound affected to some people.
Thanks so much for your explanation. For non-native speakers, we usually think of stress and tone as the same thing. So I tend to use a higer tone for stressed syllable and normal or lower tone for unstressed syllable.
It is easy for us to learn the correct stress as it is given in the dictionary. But it is hard to learn the correct use of tones. And I notice that tone seems a key factor to determine the accent, since the tone makes non-native speakers' accent sound distinctively different from native speakers.
So I would like to know if there is hidden rules for the choice of tones? For example, in what circumstance or context shall we adopt the kind of tone as mentioned above?
That's a hard one. Stress and tone are completely unrelated in English. Tonal patterns also vary immensely between dialects of English, as they are not constrained by needing to mean something. So the melody of each dialect changes, even when the same things is being said. So it's really impossible to tell you any real "rules" for pitch and tone, because they will change from one accent to another!
You can get a feel for this changing quality in this youtube video where she addresses how you use variations in pitch to successfully mimic different accents (about 3 minutes in):
Here the same woman says the same thing over and over in different accents, and you can hear the variations in tone and pitch in the same sentence:
Pitch changes do convey emotion or indicate a question -- questions usually end on a rising pitch, while statements end on a falling pitch.
I like to use the word ''INTONATION'' to show what intonation is.
In english the stress is put on the third syllable as in ''intoNation''.
In spanish it is on the forth syllable as in ''intonaTIon''.
In french there is no word intonation as in ''intonation''; only the end of the sentence will accept a change unless you realy want to express things.
As a french canadian, I have spoken english for thirty years as a second language and they (the anglos) still comment on my bad intonation even thought they don't know what to call it.
In spanish the rules are clearly establised and any grammar will explain it.
In english I believe you must memorize it.
So the only the thing I have to know in order to master the intonation of a language is where to put the stress in a word? I wish it were as easy as that, but it's not.
Your experience with English speakers should have shown you that. You probably know where to put the stress in English words but English speakers still comment on your bad intonation as you say. Isn't that a pretty obvious sign that there's more to intonation than just stress?
Intonation is the melody of a phrase. The video Uriel's linked to shows it pretty well (starting at 3:30).
You can't show what intonation is if you're using only one word. That leads to the thought that intonation and stress are the same thing (which they're not).