Sentence stress refers to the stronger accent on certain words in spoken English within a sentence. It is similar to word stress but the word stress refers to the accent of one syllable within a word.
In English language not all words within a sentence get the same accent or stress, or in other words, they are not pronounce with the same intensity. This is one of the reasons why foreign speakers of English have accents that are different than of those who are English native speakers.
Sentences in English language are formed from two kinds of words. They are content words and structure words.
Content words as the name suggests, are the words that give the sentence its meaning. They are very important and without one of them the listener may not understand the meaning of the sentence.
Structure words don’t have anything to do with the meaning of the sentence, so they are considered less important. However, they make the sentence to be correct from grammar point of view. Removing one or more structure words probably won’t change the meaning of the sentence.
I want to buy a computer because mine is broken.
I marked the content words and eliminating the other words will read: want buy computer mine broken. It is perfectly understandable.
There are three basic rules regarding sentence stress.
Usually, words that carry the meaning and are cataloged as content words, are: main verbs (teach, drive etc), nouns (computer, horse etc), adjectives (blue, small etc), adverbs (loudly, always etc), and negative auxiliaries (don’t, can’t etc).
Words that are considered structure words, so they are unstressed, are: pronouns (I, you etc), prepositions (under, below etc), articles (a, an, the), conjunctions (and, but etc), and auxiliary verbs (do, be etc).