What is sentence stress?
In English, some words are spoken more strongly and are easier to hear, and some words are spoken quickly, or weakly, and can be hard to hear clearly. This combination of weak words and strong words in a sentence, makes a kind of rhythm which is called sentence stress.
Here is a sentence to demonstrate: We have to put all the bags in the car now.
Now, I will say that same sentence without sentence stress (as best I can): We have to put all the bags in the car now. It doesn’t sound natural that way, even though I said all of the vowels and consonants correctly.
Normally, that sentence would have 3 strong words: “put”, “bags”, and “car”. Those words are clear and easy to hear. The other words are spoken quickly, and may be reduced, so that they can be said more easily. This is why “have to” sounds like “hafta”: We have to put all the bags in the car now.
This combination of weak and strong words, gives English a special kind of rhythm. Linguists call this “stress-timing.” Sometimes the strong words can form a series of beats that you can clap with: We have to put all the bags in the car now.
The basic rule of sentence stress, is that the strong words should be the ones that are the most important for the meaning of the conversation. Therefore, nouns and verbs are the primary strong words, and the foundation of sentence stress.