Sentence rhythm, weak words and linking

In I can swim, can is usually a quick /kən/; in I can't swim, can't stays strong.

Words have stress, and sentences have stress too. In a normal English sentence, the important words are strong and the small grammar words are weak. Important words, often called content words, carry the meaning: nouns, main verbs, adjectives, adverbs and question words like what. Grammar words, often called function words, hold the sentence together: a, the, to, of, and, can, is, at, for. When people speak at normal speed, the strong words come at a fairly steady beat and the weak words are squeezed between them.

Weak forms

Many function words have two pronunciations: a strong form, used when the word is said alone or with emphasis, and a weak form, used inside sentences. The weak form usually has schwa. To is /tuː/ alone but /tə/ in I want to go. And is /ænd/ alone but often /ən/ in fish and chips. Of becomes /əv/ in a cup of tea. Can becomes /kən/ in I can swim. Learner dictionaries such as Cambridge list both forms for these words.

This matters for listening as much as speaking. If you expect to hear a clear and or to, you may miss them completely. It also helps you hear the difference between can and can't in American English. In a positive sentence, can is weak: I can come, /aɪ kən kʌm/. Can't is never weak. It keeps its full vowel and is usually stressed: I CAN'T come, /aɪ kænt kʌm/. The final t is often very soft, so listen for the strong vowel.

Linking

English speakers do not stop between words. When a word ends in a consonant and the next word starts with a vowel, the consonant moves across: an apple sounds like a napple, turn it off sounds like tur-ni-toff, and pick it up sounds like pi-ki-tup. When two vowels meet, a small y or w sound often joins them: I am sounds like I-yam, and go out like go-wout. Linking makes speech smooth. You do not need to change the words, only to let them run together.