Four hu

The four hu (Chinese: 四呼; pinyin: sì hū) are a traditional way of classifying syllable finals of Mandarin dialects, including Standard Chinese, based on different glides before the central vowel of the final. They are

• kāikǒu (開口, "open mouth"), finals without a medial
• qíchǐ (齊齒, "even teeth"), finals beginning with [i]
• hékǒu (合口, "closed mouth"), finals beginning with [u]
• cuōkǒu (撮口, "round mouth"), finals beginning with [y]

The terms kāikǒu and hékǒu come from the Song dynasty rime tables describing Middle Chinese. The Qing phonologist Pan Lei divided each of these categories in two based on the absence or presence of palatalization, and named the two new categories.

This traditional classification is reflected in the bopomofo notation for the finals, but less directly in the pinyin:

Four hu table

Kāikǒu				Qíchǐ				Hékǒu				Cuōkǒu
IPA	Bopomofo	Pinyin		IPA	Bopomofo	Pinyin		IPA	Bopomofo	Pinyin		IPA	Bopomofo	Pinyin
a	ㄚ	a		ia	ㄧㄚ	ia		ua	ㄨㄚ	ua
ɤ	ㄜ	e		ie	ㄧㄝ	ie		uo	ㄨㄛ	uo		ye	ㄩㄝ	üe
ɨ	ㄭ	-i		i	ㄧ	i		u	ㄨ	u		y	ㄩ	ü
ai	ㄞ	ai						uai	ㄨㄞ	uai
ei	ㄟ	ei						uei	ㄨㄟ	wei/-ui
au	ㄠ	ao		iau	ㄧㄠ	iao
ou	ㄡ	ou		iou	ㄧㄡ	you/-iu
an	ㄢ	an		iɛn	ㄧㄢ	ian		uan	ㄨㄢ	uan		yɛn	ㄩㄢ	üan
ən	ㄣ	en		in	ㄧㄣ	in		uən	ㄨㄣ	wen/-un		yn	ㄩㄣ	ün
aŋ	ㄤ	ang		iaŋ	ㄧㄤ	iang		uaŋ	ㄨㄤ	uang
əŋ	ㄥ	eng		iŋ	ㄧㄥ	ing		uəŋ	ㄨㄥ	weng
ʊŋ	ㄨㄥ	-ong		iʊŋ	ㄩㄥ	iong
aɚ	ㄦ	er