Ido phonology

Ido has five vowel phonemes. The vowels and  are interchangeable depending on speaker preference, as are  and. The combinations /au/ and /eu/ become diphthongs in word roots but not when adding affixes.

All polysyllable words are stressed on the second-to-last syllable except for verb infinitives, which are stressed on the last syllable – skolo, kafeo and lernas for "school", "coffee" and the present tense of "to learn", but irar, savar and drinkar for "to go", "to know" and "to drink". If an i or u precedes another vowel, the pair is considered part of the same syllable when applying the accent rule – thus radio, familio and manuo for "radio", "family" and "hand", unless the two vowels are the only ones in the word, in which case the "i" or "u" is stressed: dio, frua for "day" and "early".