In any sentence, not all words receive equal stress — content words (nouns, main verbs, adjectives, adverbs) are typically stressed, while function words (articles, prepositions, pronouns, auxiliary verbs) are typically unstressed and reduced. “Ik HEB een BOEK geKOCHT” — heb and een are reduced; boek and kocht carry the sentence stress. This rhythm of alternating stressed and unstressed syllables is fundamental to Dutch sounding natural.
Focus stress is placed on the word that carries the most important new information. In response to “What did you buy?”: “Ik heb een BOEK gekocht” — boek gets the focus. In response to “Who bought a book?”: “IK heb een boek gekocht” — ik gets the focus. Misplacing focus stress sends confusing signals to native speakers about what is new or important in your message.
Contrastive stress corrects a misunderstanding: if someone says you live in Amsterdam and you live in Rotterdam: “Nee, ik woon in ROTTERDAM, niet in Amsterdam.” Rotterdam gets heavy contrastive stress. Dutch native speakers use this kind of emphatic stress constantly and naturally — understanding it helps you follow conversations and use it yourself to be clear and emphatic when needed.