* "[O]ne of the functions of phonetic stress is to make words understandable. This kind of stress, known as word-level stress, is actually part of a word's pronunciation. It may also serve to differentiate words that are similar. For example, We're going to record a record, the two similar words are stressed differently so that the first record is stressed on the second syllable (vowel reduction in the first syllable also assists in helping us to assign stress to the second syllable), whereas the second record is stressed on the first syllable (with vowel reduction in the second syllable). All words of more than one syllable have a prominent or stressed syllable. If we pronounce a word with appropriate stress, people will understand us; if we use the wrong stress placement, we run the risk of being misunderstood.
"Phrase or sentence stress is tied to meaning, and this is the second function of stress. As we focus a camera on some item ...view middle of the document...
(Peter Ladefoged and Keith Johnson, A Course in Phonetics, 6th ed. Wadsworth, 2011)
* Stress With Content Words and Function Words
"[T]he words most likely to receive sentence stress are those termed content words (also called 'lexical words'), namely nouns, adjectives, adverbs, and main verbs. These are the words that normally carry a high information load. We can contrast these with function words (also called 'grammar words' or 'form words'), namely determiners (e.g. the, a), conjunctions (e.g. and, but), pronouns (e.g. she, them), prepositions (e.g. at, from), auxiliary verbs (e.g. do, be, can). Function words carry relatively little information; their role is holding the sentence together. . . . Unlike content words, function words for the most part carry little or no stress. Only two types of function words are regularly stressed: the demonstratives (e.g. this, that, those) and wh- interrogatives (e.g. where, who, which, how). Note, however, that when wh- words and that are used as relatives they are unstressed, e.g. the girl who lent me the yellow hat that I wore to your wedding."
(Beverley Collins and Inger M. Mees, Practical Phonetics and Phonology: A Resource Book for Students. Routledge, 2003)
* Lexical Diffusion
"Some linguistic change first manifests itself in a few words and then gradually spreads through the vocabulary of the language. This type of change is called lexical diffusion. A well-attested example in English involves an ongoing change in the stress pattern of words such as convert, which can be used as either a noun or a verb. Although the stress originally fell on the second syllable regardless of lexical category, in the latter half of the sixteenth century three such words, rebel, outlaw, and record, came to be pronounced with the stress on the first syllable when used as nouns. . . .
"This change has still not diffused through the entire vocabulary of English. There are about a thousand nouns of the relevant sort that still place the stress on the second syllable (e.g., report, mistake, and support)."
(William O'Grady et al., Contemporary Linguistics: An Introduction, 4th ed. Bedford/St. Martin's, 2001)