Up to three tonic syllables may occur together, but the number of resulting tones is reduced by tone sandhi. Of the six phonetic tones, there are only fourteen lexical patterns created by two tonic syllables. With one exception, the "shǎng" and "qù" tones reduce to HM ("yīn qù") before any other tone, and again with one exception, the "rù" tone does not interact with a following tone. The "shǎng" and "rù" tones change a preceding non-"rù" tone to HM, and are themselves never affected.