It is usually said that there are six vowels in Indonesian. These six vowels are shown in the table below. However, other analyses set up a system with other vowels, particularly the open-mid vowels /ɛ/ and /ɔ/.
In standard Indonesian orthography, the Latin alphabet is used, and five vowels are distinguished: a, i, u, e, o. In materials for learners, the mid-front vowel /e/ is sometimes represented with a diacritic as é to distinguish it from the mid-central vowel /ə/.
Some analyses claim that Indonesian has three native diphthong phonemes only in open syllables, they are:
- /ai̯/: kedai ('shop'), pandai ('clever')
- /au̯/: kerbau ('buffalo'), limau ('orange')
- /oi̯/ (or /ʊi̯/ in Indonesian): dodoi, amboi
Others assume that these "diphthongs" are actually a monophthong followed by an approximant, so ⟨ai⟩ represents /aj/, ⟨au⟩ represents /aw/, and ⟨oi⟩ represents /oj/. On this basis, there are no phonological diphthongs in Indonesian.
Diphthongs are differentiated from two vowels in two syllables, such as:
- /a.ʔi/: e.g. rayakan ('celebrate') [ra.ʔi], air ('water') [a.ʔer] (or [a.ʔɪr] in Indonesia and [a.ʔir] elsewhere)
- /a.ʔu/: bau ('smell') [ba.ʔu], laut ('sea') [la.ʔot] (or [la.ʔʊt] in Indonesia and [la.ʔut] elsewhere)
The consonants of Indonesian are shown below. Non-native consonants that only occur in borrowed words, principally from Arabic and English, are shown in parentheses. Some analyses list 19 "primary consonants" for Indonesian as the 18 symbols that are not in parentheses in the table as well as the glottal stop [ʔ].
The sounds are represented orthographically by their symbols as above, except:
- /ɲ/ is written ⟨ny⟩ before a vowel, ⟨n⟩ before ⟨c⟩ and ⟨j⟩
- /ŋ/ is written ⟨ng⟩
- the glottal stop [ʔ] is written as a final ⟨k⟩ or an apostrophe ⟨'⟩ (the use ⟨k⟩ from its being an allophone of /k/ or /ɡ/ in the syllable coda)
- /tʃ/ is written ⟨c⟩
- /dʒ/ is written ⟨j⟩
- /ʃ/ is written ⟨sy⟩
- /x/ is written ⟨kh⟩
- /j/ is written ⟨y⟩
Indonesian has light stress that falls on either the final or penultimate syllable, depending on regional variations as well as the presence of the schwa (/ə/) in a word. It is generally the penultimate syllable that is stressed, unless its vowel is a schwa /ə/. If the penult has a schwa, then stress moves to the ante-penultimate syllable if there is one, even if that syllable has a schwa as well; if the word is disyllabic, the stress is final. In disyllabic stress with a closed penultimate syllable, such as tinggal ('stay') and rantai ('chain'), stress falls on the penult.
However, there is some disagreement among linguists over whether stress is phonemic (unpredictable), with some analyses suggesting that there is no underlying stress in Indonesian.
The classification of languages based on rhythm can be problematic. Nevertheless, acoustic measurements suggest that Indonesian has more syllable-based rhythm than British English, even though doubts remain about whether the syllable is the appropriate unit for the study of Malay prosody. However, many linguists suggest that rhythm in Indonesian is not payed, because Indonesian is not a kind of tonal language like Chinese, Thai, or Vietnamese.