in this position. The final, which occurs only after dental sibilant and retroflex initials, is a syllabic approximant, prolonging the initial. The rhotacized vowel forms a complete syllable. A reduced form of this syllable occurs as a sub-syllabic suffix, spelled -r in pinyin and often with a diminutive connotation. The suffix modifies the coda of the base syllable in a rhotacizing process called erhua. Each full syllable is pronounced with a phonemically distinctive pitch contour. There are four tonal categories, marked in pinyin with iconic diacritic symbols, as in the words (; "mother"), (; "hemp"), (; "horse") and (; "curse"). The tonal categories also have secondary characteristics. For example, the third tone is long and murmured, whereas the fourth tone is relatively short. Statistically, vowels and tones are of similar importance in the language. There are also weak syllables, including grammatical particles such as the interrogative ma () and certain syllables in polysyllabic words. These syllables are short, with their pitch determined by the preceding syllable. Such syllables are commonly described as being in the neutral tone. Regional accents It is common for Standard Chinese to be spoken with the speaker's regional accent, depending on factors such as age, level of education, and the need and frequency to speak in official or formal situations. This appears to be changing, though, in large urban areas, as social changes, migrations, and urbanization take place. Due to evolution and standardization, Mandarin, although based on the Beijing dialect, is no longer synonymous with it. Part of this was due to the standardization to reflect a greater vocabulary scheme and a more archaic and "proper-sounding" pronunciation and vocabulary. Distinctive features of the Beijing dialect are more extensive use of erhua in vocabulary items that are left unadorned in descriptions of the standard such as the Xiandai Hanyu Cidian, as well as more neutral tones. An example of standard versus Beijing dialect would be the standard (door) and Beijing . Most Standard Chinese as spoken on Taiwan differs mostly in the tones of some words as well as some vocabulary. Minimal use of the neutral tone and erhua, and technical vocabulary constitute the greatest divergences between the two forms. The stereotypical "southern Chinese" accent does not distinguish between retroflex and alveolar consonants, pronouncing pinyin zh [tʂ], ch [tʂʰ], and sh [ʂ] in the same way as z [ts], c [tsʰ], and s [s] respectively. Southern-accented Standard