Introduction

Please consider the information from footnotes as optional, as they're not needed to understand the article. They contain either comments on decisions I made, or trivia for advance Japanese speakers.

Definitions

In order to facilitate and streamline the explanation of pitch accent behaviour in Japanese, the following terms are used

Mora

A mora is the shortest unit of length in Japanese phonology. Every open syllable is a mora, long syllables are two moras¹, even if spelled with ー. ん and っ are also considered separate moras. A rule of thumb is, when written in kana, each character represents a separate mora (with an exception of small ゃゅょ and sometimes ぁぃぅぇぉ)

Word	Reading	Moras	Mora count	Explanation
先生	せんせい	せ・ん・せ・い	4	ん is always a separate mora
優しい	やさしい	や・さ・し・い	4	い is its own mora even though it makes し long
合唱	がっしょう	が・っ・しょ・う	4	っ is always a separate mora; しょ is one mora because ょ only changes the vowel from i to o
です	です	で・す	2	す is its own mora even if pronounced with voiceless u
パーティー	パーティー	パ・ー・ティ・ー	4	ー is always a separate mora (long vowels are two moras long); ティ is one mora because ィ only changes the vowel from e to i
さぁ	さあ	さ・あ	2	Even though ぁ is a small kana character, it's used here to make さ long, therefore it is considered a separate mora

Phrase

A phrase is part of a sentence with distinct meanign and gramatical function, which has it's own pitch accent. Contrary to common belief, pitch accent doesn't apply to words but to entire phrases in a sentence. A phrase usually consist of a core meaning word (usu. noun/verb/adjective) and it's prefixes, suffixes, particles, and conjugation endings.

Let's look at this sentence:

山口さんは日本人ですか

Being very generous one could split this sentence into these separate words

山口　さん　は　日本人　です　か

However, this sentence consists of only two phrases:

山口さんは　日本人ですか

Where:

• 山口さんは
  • 山口 – core meaning word (surname)
  • 〜さん – suffix (honorific)
  • 〜は – particle (topic)
• 日本人ですか
  • 日本人 – core meaning word
  • 〜です – copula (to be)
  • 〜か – particle (question)

Therefore the whole sentence would be stressed like this:

やまぐちさんは　にほんじんですか²

And not

やまぐち　さん　は　にほんじん　です　か

Stressed mora

It's the last high mora before a downstep. Note that if there's no downstep (heiban), the final mora is not stressed. In this wiki, stressed moras are marked in red. Examples:

• せんせい (先生) - せ is the last high mora, so it's stressed
• アニメ - ア is the last high mora, so it's stressed
• はな (花) - な is the last high mora (the downstep is still there because it's odaka)
• わたし - no stressed mora (し is the last high mora but there's no downstep after it)

An expression "X is stressed" is equivalent to "X is a stressed mora", and by extension "X is the last high mora and after it there's a downstep"

Stressed word/phrase

It's a word/phrase which has a stressed mora. In practice, heiban is consider non-stressed and atamadaka, nakadaka, and odaka are considered stressed

Weak mora

It's a mora which cannot be stressed, even if it otherwise would following the regular rules. っ and ん are never stressed and therefore are considered weak. Additionaly, for some long vowels/glides the second mora is considered weak, but it's not always the case. Examples:

• せんせい (先生) - ん and い are weak moras
• おおい (多い) - the second お is a weak mora as it's the second mora in the long o
• かえる (帰る) - え is a weak mora as it's the second mora of the ae glide

In almost every case, when a weak mora needs to be stressed, the stress moves one mora back:

• しゃかいじん (社会人) not しゃかいじん, because い is a weak mora.

Types of phrases

Noun phrases

Stressed nouns

After stressed nouns, most postpositions will follow the low pattern:

• せんせい
• せんせいは
• せんせいの
• せんせいに
• せんせいから
• せんせいには
• せんせいです
• せんせいですよね

Keep in mind it also applies to odaka:

• はな
• はなは
• はなですよね

One very important exception is 日本 when paired with 〜の:

• にほん
• にほんは
• にほんの !!!

Non-stressed nouns

After non-stressed (heiban) nouns, the behaviour is different based on how long the whole postposition is. If it's only one mora, it keeps its heiban pattern:

• わたし
• わたしは
• わたしの
• わたしに
• わたしと

However, if the whole postposition is two or more moras long, the first mora of the postposition is stressed:

• わたしには
• わたしです
• わたしなのよ
• わたしまで

Two important exceptions from this rule are 〜から and 〜だけ, which behave like one mora particles³:

• わたしから ・わたしだけ
• わたしからです・わたしだけです
• わたしからの ・わたしだけの
• わたしからには・わたしだけには

Na-adjective phrases

Generally, the same rules as for nouns apply. So for stressed na-adjectives the pattern continues with the low pitch:

• きれい
• きれいな
• きれいに
• きれいですね

While for heiban, only the first mora of the postposition is high:

• かんたん
• かんたんな
• かんたんに
• かんたんですよ

Please note that the negation of na-adjectives (and also nouns for this matter) isn't considered a single phrase and therefore the above rules do not apply⁴:

• きれいじゃ　ない
• かんたんじゃ　ない

I-adjective phrases

The vast majority of i-adjectives are stressed, and the stress falls on the penultimate (second to last) mora, therefore they all behave the same.

Postpositions which are not changing the adjective (particles, です etc.) stay low:

• いい
• いいです
• いいね

Verb phrases