Stress and the Tonos
Modern Greek is monotonic: a single accent mark, the tonos (´), sits over the vowel of the stressed syllable, and every word of two or more syllables carries exactly one. The stress can fall on one of the last three syllables, and where it lands can change a word’s meaning - so the tonos is information, not decoration. (A second mark, the dieresis ¨, only signals that two vowels are read separately.)
The rule
Modern Greek is monotonic - one accent, the tonos (´), over the vowel of the stressed syllable. Every word of two or more syllables carries exactly one tonos, and it may fall only on one of the last three syllables. The mark is information, not decoration: moving it can change the word. A separate mark, the dieresis (¨), is not stress at all - it only signals that two vowels are read separately.