How to pronounce I'm reading a biography of a famous scientist. in American English

That's the flap-T rule: when /t/ sits between two vowels — inside a single word, or across the boundary between two words — Americans replace the crisp T with a quick D-like flap. It's one of the most distinctive sounds of casual American speech and one of the first things to copy if you want to sound less textbook.

Function words — articles, prepositions, auxiliaries, pronouns — reduce to short, unstressed schwa shapes in casual American speech. Pronouncing them fully like the dictionary entry is a dead giveaway of a textbook accent. Native speakers stress only the content words and let everything else collapse.

Americans don't pause between words. A consonant at the end of one word links forward into the vowel that starts the next; two vowels in a row get bridged by a tiny W or Y glide; an identical consonant repeated across a word boundary is held just once. The result is a continuous flow rather than a textbook word-by-word delivery.

Textbooks usually teach the citation form — every word pronounced fully, every consonant crisp, every vowel pure. Americans actually flap their Ts, drop function-word H's, link consonants forward into vowels, and reduce unstressed syllables to schwa. The respell on this page shows the casual form you'll hear in real conversations rather than the textbook version.