Broadly speaking, in initial syllables the Indo-European simple vowels—"(*a), *e, *i, *o, *u"; short and long—are usually retained in Latin. The schwa indogermanicum ("*ə") appears in Latin as "a" (cf. IE "*pəter" > L "pater"). Diphthongs are also preserved in Old Latin, but in Classical Latin some tend to become monophthongs (for example "oi" > "ū" or "oe", and "ei" > "ē" > "ī"). In non-initial syllables, there was more vowel reduction. The most extreme case occurs with short vowels in medial open syllables (i.e. short vowels followed by at most a single consonant, occurring neither in the first nor last syllable): All are reduced to a single vowel, which appears as "i" in most cases, but "e" (sometimes "o") before "r", and "u" before an "l" which is followed by "o" or "u". In final syllables, short "e" and "o" are usually raised to "i" and "u", respectively.