The language possesses five vowels (or six, under the St. Petersburg Phonological School), which are written with different letters depending on whether or not the preceding consonant is palatalized. The consonants typically come in plain vs. palatalized pairs, which are traditionally called hard and soft. (The hard consonants are often velarized, especially before front vowels, as in Irish). The standard language, based on the Moscow dialect, possesses heavy stress and moderate variation in pitch. Stressed vowels are somewhat lengthened, while unstressed vowels tend to be reduced to near-close vowels or an unclear schwa. (See also: vowel reduction in Russian.)