Rules for Pronunciation changes in Japanese

Voiced Consonants: Dakuon 濁音

The unvoiced ka, sa, ta, ha series can be made voiced as ga, za, da, ba by adding a diacritic as in か to が, さ to ざ, た to だ, は to ば and so forth. When this occurs as a sound shift, it happens, albeit inconsistently, in the following cases:
  1. In proper names and and compound words when the の is dropped, and the following consonant made voiced
  2. In 百, 千, and 本, when they occur after the number three
  3. In certain compound word idioms
Rule Individual Pronunciations Combined Pronunciation Romaji Kanji Translation
1 すみだのかわ すみだがわ sumidagawa 隅田川 the Sumida River
1 やぎのしる やぎじる yagijiru 山羊汁 lamb stew
2 さん + ひゃく さんびゃく sanbyaku 三百 three hundred
2 さん + せん さんぜん sanzen 三千 three thousand
2 さん + ほん さんぼん sanbon 三本 three long, thin things
3 とう + さん とざん tozan 登山 hiking
3 たち + くい たちぐい tachigui 立ち食い a standing-only restaurant
3 あじあ + ちゅう あじあじゅう ajiajyuu アジア中 throughout Asia

Consonant Lengthening: Sokuon 促音

  1. In kanji compounds, when (on-reading) pronunciation of a kanji ends in ち or つ, and the following consonant is unvoiced and from the ka, sa, or ta serieses, the ち or つ are dropped and the lengthening of the following consonant is indicated by a writing small tsu (っ).
  2. In verbal compounds when conjugation of the first verb calls for aり or き syllable, and the following consonant is not this syllable is dropped, and the lengthening of the following consonant is indicated by a writing small tsu (っ).
Rule Individual Pronunciations Combined Pronunciation Romaji Kanji Translation
1 しゅつ + か しゅっか shukka 出荷 to ship out cargo
1 せつ + たい せったい settai 接待 to entertain (guests)
2 ひき + はる ひっぱる hipparu 引っ張る to pull taught
2 ふち + とばす ふっとばす futtobasu ぶっ飛ばす to shake off with force

Handaku 半濁

The ha, hi, fu, he, ho (はひふへほ and ハヒフヘホ) sounds were originally pa, pi, pu, pe, po, sounds which are today indicated by a circle handaku diacritic (ぽぴぷぺぽ、パピプペポ). The sounds shifted as a result of a process linguists call bilabial dissimilation, enabling modern speakers of foreign languages to marvel at how it's possible for many Japanese to speak with a minimum of mouth movement.

In modern standard Japanese, the unvoiced pa, pi, pu, pe, po handaku pronunciations occur in these cases:
  1. Following a nasal n ん, except after "four"よん
  2. Sokuon and Handaku: In kanji compounds, after a kanji whose the pronunciation ends in ち or つ, and the following consonant is not voiced, the ち or つ are dropped and the lengthening of the following handaku consonant is indicated by a writing small tsu (っ).

Rule Individual Pronunciations Combined Pronunciation Romaji Kanji Translation
1 しん + はん しんぱん shinpan 審判 to judge
1 しん + はい しんぱい sinpai 心配 to worry
2 いち + はん いっぱん ippan 一般 generally
2 しゅつ + はつ しゅっぱつ shuppatsu 出発 to depart
3 ひき + はる ひっぱる hipparu 引っ張る to pull taught
3 ふり + とばす ふっとばす futtobasu ぶっ飛ばす

Note that the handaku pronunciation rules are inconsistent across the dialects, so that while the Fukuoka dialect has よんぴゃく for "four hundred," modern standard Japanese has よんひゃく (without the handaku).