Japanese parsing

parsing using the reader’s knowledge

Consider the kanjis in the following sign:

kanji words are not separated with spaces

As the English translation in the above sign shows, these eight kanjis represent four words but… what kanjis represent each of the words? Some words might be a single kanji long, like 日 (‘hi’, sun); some others words might be two kanjis long, like 日本 (‘ni-hon’, Japan); while some others might be three kanjis long, like 日本語 (‘ni-hon-go’, the Japanese language). So how do we know which characters are part of a word, and which ones are not? How do Japanese people split a sequence of characters – kanjis or kanas – into separate words?

The process of separating a sequence of characters or sounds into a meaningful sequence of individual units, a.k.a. tokens, is called ‘parsing’, and it’s one of the main difficulties of understanding a new language, specially when listening. The reason we pronounce words slowly and separately when we are trying to be clear about what we are saying is to facilitate our listener the parsing of our words; we are duplicating the role of the spaces in written language with pauses in the spoken language. We start getting really good at understanding a new language when we are able to do this parsing on the fly.

English separates words with spaces, but Japanese doesn’t use any separators:

Tokyo Med. Univ. Hospital
thank you very much
vanilla ice cream

toukyou ika daigaku byouin
doumo arigatou gozaimasu
banira aisu kuriimu


Sequences of words written in either kanji or hiragana, like ‘Tokyo Medical University Hospital’ or ‘thank you very much’, are never separated and, instead, the reader must already know how to split the text, i.e., how to parse the sentence into words. It is like reading ‘tokyomedicaluniversityhospital’ and ‘thankyouverymuch’; it’s cumbersome but doable, and with practice we would get used to it.

We usually don’t separate words in katakana, either. However, we often separate the first name and last names of people with a dot, ‘・’, the Japanese equivalent of the English dash; we could also add dots if we want to make something extra clear, but in general, there is no separation:

John Wayne
Frank Sinatra

Australian dollar (v1, w/ dot)
Australian dollar (v2)

Buenos Aires
Los Angeles

jon uein
furanku shinatora

oosutoraria doru





Writing systems as word separators

We can write any Japanese word using only hiragana or katakana; either of them would suffice. However, normally we write nouns, adjectives, and verb roots in kanji, while we write verb suffixes and particles in hiragana. Thus, given the absence of spaces, a combination of kanjis and kanas helps us to parse sentences because we roughly know what kanjis and kanas generally represent. For example:


Mr. Tanaka drinks coffee.
tanaka san wa kouhii wo nomi-masu

In this sentence, the noun ‘Tanaka’ (田中) is written in kanji; the stem of the verb ‘drinks’ (飲み) is written in kanji and hiragana; the honorific ‘Mr.’ (さん), the particles that mark the topic (は) and object (を), and the verb’s suffix of ‘drinks’ (ます) are written in hiragana; and the foreign-origin word ‘coffee’ (コーヒー) is written in katakana. Hence, the writing systems cue us about the nature of the words. To make this clear, let’s see the sentence again, color-coding the kanjis, hiraganas and katakanas:


Mr. Tanaka drinks coffee.
tanaka san wa kouhii wo nomi-masu


The parsing is not perfect; in our example, using multiple writing systems doesn’t separate ‘san’ and ‘wa’ into different words, and splits ‘nomi’, which is a verb stem, into ‘no’ and ‘mi’. Still, even though different writing systems place boundaries on some words, we still need some previous knowledge of Japanese to parse the complete sentence.

Word-particle parsing

We can also parse a sentence knowing that, in Japanese, words are often clustered in word-particle sets. A particle defines the role of the word that precedes it so, in general, they form clusters that we can move around and still be gramatically correct. For example, は and を indicate the topic and the object, respectively; the verb stands on its own, without a particle, but we can identify it because it starts with a kanji and ends in a syllable that ends in ‘u’. Thus, for topic, object and verb we have:

Sentence part

(Tanaka san wa)
(kouhii wo)


Since the function of each word-particle set is defined, we can move the sets around and still have a gramatically correct sentence, i.e., all of the following sentences are grammatically correct, although the first one sounds the most natural in Japanese because in Japanese the verb usually closes the sentence:

(Mr. Tanaka) (coffee) (drinks)
(coffee) (Mr. Tanaka) (drinks)
(coffee) (drinks) (Mr. Tanaka)

(Tanaka san wa) (kouhii wo) (nomi-masu)
(kouhii wo)、(Tanaka san wa) (nomi-masu)
(kouhii wo) (nomi-masu)、(Tanaka san wa)

The result is that we can parse a sentence by looking for the particles and clustering them with the words that precede them. Although this works well in many cases, there are two issues. The first one is that Japanese has few sounds and few particles, so many of the particles are overworked and it might be difficult to tell them apart for parts of words. For example, consider the particle に (ni) in the following sentence:


This is a sentence that even a Japanese person would have to read slowly to make sense of; indeed, it is easier to parse it if we introduce kanjis because the particles stand out:


あにあいにほんにがついきます (Google translate fails)
兄に合いに日本に二月に行きます (Google translate succeeds)
ani ni ai ni nigatsu ni nihon ni ikimasu
In February I am going to Japan to see my big brother

Or good luck parsing this extreme case of a fun tongue-twister:


Let’s see:


sumomo mo momo mo momo no uchi
Both the plum and the peach are in the peach family

The second problem with parsing sentences using particles is that it only works well with formal speech because casual speech drops many particles:

formal speech
Tanaka san wa kouhii wo nomimasu

casual speech
Tanaka san kouhii nomu

Both of these sentences are identical in meaning but the second one has no particles at all so we cannot make word-particle sets and, instead, we have to parse the sentence relying only on our knowledge of Japanese and its writing systems.

Multiple writing systems in a word

Consider the following newspaper article:

Various punctuation marks

Usually, we write the stem of the verb in kanji (or kanji and hiragana) and the suffix in hiragana, like in 飲みます (nomi-masu – to drink); the same happens with adjectives, i.e., the stem is in kanji (or kanji and hiragana), and the suffix is in hiragana, like in 大きい (ooki-i – big). Nouns are often in kanji, but sometimes a part of a noun is in kanji and the rest in hiragana, e.g., in a red box in the article, we find the word ‘kodomo’ (children); we could write ‘ko-domo’ using two kanjis, 子供, but the writer has chosen to write the first character of the word, 子 (ko), in kanji, and the rest of the word in hiragana, ども (domo), so in spite that ‘children’ is a noun, in this case, the use of kanjis and kanas doesn’t help us to identify the end of the word. In all of these cases, the hiragana characters that finish the word started with the kanji are called okurigana, e.g.,

to drink


kanji + okurigana

Although not so common, a single word can also be a combination of kanji, hiragana, and katakana. For example, the word ‘keshigomu’ (eraser) combines the Japanese word ‘keshi’ (消し – to erase), in kanji and hiragana, and the foreign-origin word ‘gomu’ (ゴム – gum, or rubber), in katakana; the word ‘denshirenji’ (microwave) combines the Japanese word ‘denshi’ (電子 – electronic) in kanji and hiragana, and the foreign-origin word ‘renji’ (レンジ – range), in katakana. Also, in some cases the word might begin with hiragana and end in a kanji, e.g., ‘tameiki’ (sigh) starts with ‘tame’ (to collect) and ends in ‘iki’ (息 – breath).

microwave oven


ゴム (kanji + hiragana + katakana)
レンジ (kanji + hiragana + katakana)
ため (hiragana + kanji)

Roman characters have also found their way as part of a few Japanese words, e.g., we can write T-shirt either in katakana, or using the roman letter:



ティーシャツ (katakana)
シャツ (roman + katakana)

Hence, in general we can use kanjis to parse the beginning of nouns, but there are plenty of exceptions.

Punctuation marks

In addition to the use of kanji vs. kanas for word parsing, Japanese uses punctuation marks to parse sentences and sentence fragments. We can see in the annotated newspaper article some of the following Japanese equivalents of the roman punctuation marks:

  1. periods: 。。。(little circles instead of dots)
  2. commas: 、、、(Japanese commas point forward, roman commas point backwards)
  3. quotation marks: 「 」(type them with [ and ] when in hiragana mode)
  4. dash marks: ・・・ (dots play the role of dashes in a telephone number)
  5. tilde: 〜 (as shown in the schedule-box, similar to the English ~)
  6. parentheses: ( ) (oriented in the direction of the text)
  7. brackets: [ ] (oriented in the direction of the text)
  8. asterisk: (an ‘x’ with four dots around it)
  9. kanji iteration mark: (it duplicates the kanji that precedes it; for example, we can write iro-iro (various) as either 色色 or 色々)

Japanese doesn’t use hyphens to indicate that a word is split between two consecutive text rows or columns. For example, in the article, the word 大学生 (dai-gaku-sei – ‘college student’) is split between two different columns, but in the first column there is no punctuation mark similar to the hyphen that indicates that the word is split and ends in the second column.