I found it's not totally right to use only falling intonation at the end of a declarative sentences.It seems that there're some other words in the sentence use high or low or falling-rising intonation.therefore ,i am so confused about the intonation in declarative sentences.are there any rules. please notice that I just talk about declarative sentences rather than yes or no sentences or special questions.
The rules for using intonation in declarative sentences are so many and complex that it's not practical to try learning pronunciation by trying to memorize rules consciously. In fact, this is true for vocabulary and grammar also.
(Even native speaking college students do not show increased English production abilities after studying grammar. See the following article.)
The information accessible below explains the best research on learning and improving pronunciation through cognitive phonetics, though you may need to dig into the site and perform additional searches to find practically useful guidance. In brief: listen to as much native English speech as you can (speech that you can mostly understand). Then ask a native speaker to listen to you and point out where your pronunciation doesn't match. The key is to improve your listening abilities. We actually do not hear a foreign language in the same way native speakers do. For example, Chinese speakers usually don't realize that we make the a vowel sound in main for as long a duration as we do. A good English teacher can more quickly help you notice more pronunciation information in speech. But, unfortunately, few English teachers are trained in cognitive phonetics.
I can’t tell you any rules for intonation. There are some basic patterns, as shown in MARamezani’s answer, but probably no real rules at all. Whatever regularities you find will vary from region to region and dialect to dialect. However, I can tell you something about how to learn the intonation of any dialect.
There are four main things that a speaker is trying to convey through the intonation of a declarative sentence:
When the speaker has reached the end of the sentence.
When the speaker is done talking (that is, when the speaker has no more sentences to say, so it is now appropriate for someone else to talk).
Emphasis of specific words or phrases in the sentence.
Subtler things: emotion, level of certainty, social status, relationship with the listener, and more.
When listening to people speaking in conversation, try to notice how they signal these things. For example, when a person says “We rode our bikes 50 miles. We took a 20-minute break and started again," they say “miles” differently than if they just said “We rode our bikes 50 miles.” The speaker has to signal through intonation that another sentence is coming, so it’s not OK for someone else to interrupt. Similarly, “We rode fifty” has a different intonation, again to indicate that the sentence is complete.
If you try to communicate through intonation when a sentence ends and when you want to continue speaking or stop speaking, you will develop your own intonation, the same way all native speakers do. And, after some practice and adjustment, you’ll successfully communicate those things. If you try to follow rules, you’ll sound like you’re trying to follow rules.
Note that some declarative sentences function as questions, like “Guess what.” These have a different intonation than questions, but also a different intonation than ordinary declarative sentences. Again, people use intonation to communicate the intent. No two people do it quite the same way; you’ll have to discover your own way through experimentation.
One last thing: Part of picking up a dialect is paying attention to the melody of the sentences. For example, I was in central Scotland recently, and was surprised to find that a typical declarative sentence ends by rising a minor third near the end and then falling a minor third on the last syllable or two and holding it. This is very different from the progressively falling intonation common in most of the United States.
First, when we are talking about AmE English, we're talking about a very large variety of dialects and accents, and you don't seems to be looking for one of them for anyone to show you the rules, if any.
Second, situations change, and so does the thing we want to tell, so a [declarative] sentence can have different intonations due to different meanings. e.g.: Putting emphasis on the elements of the sentence changes the intonation dramatically. Look at the example below. The italic parts are the ones with emphasis:
I am very passionate about planet Earth. (1)
You state that instead of someone else, which is possibly mistakenly taken as a passionate guy about Earth, you are the passionate guy.
I am very passionate about planet Earth. (2)
Putting emphasis on the fact that you're passionate, you responded to any who thought you weren't passionate about Earth.
I am very passionate about planet Earth. (3)
You insist on the fact that you will not be mild to anyone not getting rid of their waste properly.
I am very passionate about planet Earth. (4)
You respond to people wondering about which side you're in.
I am very passionate about planet Earth. (5)
You're teaching grammar to someone! You assert that
being passionate is followed by
I am very passionate about planet Earth. (6)
"Earth is a planet, you fool!" This is what you're telling someone that thinks Earth is for example, an asteroid!
I am very passionate about planet Earth. (7)
When you emphasize on your passion being directed towards Earth, you're talking about future when someone wants your idea about a planet you're passionate about.
We have the overall intonation for the sentences above as following:
Notice that the overall into nation always tends to fall, but exceptions happen to happen to intonation. Emphasis is what that reaches my mind right now. I'm very definite there are other "intonation changers". They'll ring my bells and I'll edit my answer, or better people than me will write better answers. I personally suggest that instead of looking for a rule you might want to grasp the falling intonation concept and modify it in diverse situations.
Varying intonation can change the intent of a declarative sentence; for example read outloud:
I have never saved a lot of money.
If you stress "I", either by slight rising inflection or saying it louder, you imply someone else has saved a lot.
If you stress "lot", you imply you did save some money.
If you stress "money", you imply you have save something else, e.g. time or enjoyment.