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 - honorific suffix
  • は - particle
• 日本人ですか
  • 日本人 - core meaning word
  • です - copula
  • か - particle

Therefore the whole sentence would be stressed like this:

やまぐちさんは　にほんじんですか

And not

やまぐち　さん　は　にほんじん　です　か

Note: indicating a question by raising pitch at the end of a sentence is not a part of pitch accent analysis, and therefore will be omitted in examples

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 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 particles²:

• 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