Japanese writing system

The modern Japanese writing system uses a combination of logographic kanji, which are adopted Chinese characters, and syllabic kana. Kana itself consists of a pair of syllabaries: hiragana, used primarily for native or naturalized Japanese words and grammatical elements; and katakana, used primarily for foreign words and names, loanwords, onomatopoeia, scientific names, and sometimes for emphasis. Almost all written Japanese sentences contain a mixture of kanji and kana. Because of this mixture of scripts, in addition to a large inventory of kanji characters, the Japanese writing system is considered to be one of the most complicated currently in use.
Several thousand kanji characters are in regular use, which mostly originate from traditional Chinese characters. Others made in Japan are referred to as "Japanese kanji", also known as " country's kanji". Each character has an intrinsic meaning, and most have more than one pronunciation, the choice of which depends on context. Japanese primary and secondary school students are required to learn 2,136 jōyō kanji as of 2010. The total number of kanji is well over 50,000, though this includes tens of thousands of characters only present in historical writings and never used in modern Japanese.
In modern Japanese, the hiragana and katakana syllabaries each contain 46 basic characters, or 71 including diacritics. With one or two minor exceptions, each different sound in the Japanese language corresponds to one character in each syllabary. Unlike kanji, these characters intrinsically represent sounds only; they convey meaning only as part of words. Hiragana and katakana characters also originally derive from Chinese characters, but they have been simplified and modified to such an extent that their origins are no longer visually obvious.
Texts without kanji are rare; most are either children's books—since children tend to know few kanji at an early age—or early electronics such as computers, phones, and video games, which could not display complex graphemes like kanji due to both graphical and computational limitations.
To a lesser extent, modern written Japanese also uses initialisms from the Latin alphabet, for example in terms such as "BC/AD", "a.m./p.m.", "FBI", and "CD". Romanized Japanese is most frequently used by foreign students of Japanese who have not yet mastered kana, and by native speakers for computer input.

Use of scripts

Kanji

Kanji are logographic characters taken from Chinese script and used in the writing of Japanese.
It is known from archaeological evidence that the first contacts that the Japanese had with Chinese writing took place in the 1st century AD, during the late Yayoi period. However, the Japanese people of that era probably had little to no comprehension of the script, and they would remain relatively illiterate until the 5th century AD in the Kofun period, when writing in Japan became more widespread.
Kanji characters are used to write most content words of native Japanese or Chinese origin, which include the following:

many nouns, such as 川 and 学校
the stems of most verbs and adjectives, such as 見 in 見る and 白 in 白い
the stems of many adverbs, such as 速 in 速く and 上手 as in 上手に
most Japanese personal names and place names, such as 田中 and 東京.

Some Japanese words are written with different kanji depending on the specific usage of the word—for instance, the word naosu is written 治す when it refers to curing a person, and 直す when it refers to fixing an object.
Most kanji have more than one possible pronunciation, and some common kanji have many. These are broadly divided into on'yomi, which are readings that approximate to a Chinese pronunciation of the character at the time it was adopted into Japanese, and kun'yomi, which are pronunciations of native Japanese words that correspond to the meaning of the kanji character. However, some kanji terms have pronunciations that correspond to neither the on'yomi nor the kun'yomi readings of the individual kanji within the term, such as 明日 and 大人.
Unusual or nonstandard kanji readings may be glossed using furigana. Kanji compounds are sometimes given arbitrary readings for stylistic purposes. For example, in Natsume Sōseki's short story The Fifth Night, the author uses 接続って for tsunagatte, the gerundive -te form of the verb tsunagaru, which would usually be written as 繋がって or つながって. The word 接続, meaning "connection", is normally pronounced setsuzoku.

Kana

Kana are a set of syllabic scripts used in the Japanese writing system. The term originally means “provisional” or “borrowed names.” In modern usage, kana are primarily divided into hiragana and katakana, though historically they also included other forms such as man’yōgana and sōgana. All types of kana ultimately derive from Chinese characters: they borrow the original phonetic values of kanji and were developed from simplified forms or components of those characters.
Historically, there was no strict functional distinction between hiragana and katakana. Texts could be written in a mixture of Chinese characters and either form of kana entirely alone without a fixed division of roles. This situation changed following language reforms after World War II, which established a functional division between the two syllabaries comparable to the distinction between lowercase and uppercase letters in Western alphabetic scripts. In contemporary Japanese, the pronunciation and orthography of kana are regulated by the system known as modern kana usage.

Hiragana

Hiragana emerged as a manual simplification via cursive script of the most phonetically widespread kanji among those who could read and write during the Heian period. The main creators of the current hiragana were ladies of the Japanese imperial court, who used the script in the writing of personal communications and literature, such as the Tale of Genji.
Hiragana is used to write the following:

okurigana—inflectional endings for adjectives and verbs—such as る in 見る and い in 白い, and respectively た and かった in their past tense inflections 見た and 白かった.
Japanese particles—small, usually common words that, for example, mark sentence topics, subjects and objects or have a purpose similar to English prepositions such as "in", "to", "from", "by" and "for".
miscellaneous other words of various grammatical types that lack a kanji rendition, or whose kanji is obscure, difficult to typeset, or considered too difficult to understand for the context.
furigana—phonetic renderings of hiragana placed above or beside the kanji character. Furigana may aid children or non-native speakers or clarify nonstandard, rare, or ambiguous readings, especially for words that use kanji not part of the jōyō kanji list.

There is also some flexibility for words with common kanji renditions to be instead written in hiragana, depending on the individual author's preference. Some words are colloquially written in hiragana and writing them in kanji might give them a more formal tone, while hiragana may impart a softer or more emotional feeling. For example, the Japanese word kawaii, the Japanese equivalent of "cute", can be written entirely in hiragana as in かわいい, or with kanji as 可愛い.
Some lexical items that are normally written using kanji have become grammaticalized in certain contexts, where they are instead written in hiragana. For example, the root of the verb 見る is normally written with the kanji 見 for the mi'' portion. However, when used as a supplementary verb as in 試してみる meaning "to try out", the whole verb is typically written in hiragana as みる, as we see also in 食べてみる.

Katakana

Katakana emerged around the 9th century, in the Heian period, when Buddhist monks created a syllabary derived from Chinese characters to simplify their reading, using portions of the characters as a kind of shorthand. The origin of the system is attributed to the monk Kūkai.
Katakana is used to write the following:

transliteration of foreign words and names, such as コンピュータ and ロンドン. However, some foreign borrowings that were naturalized may be rendered in hiragana, such as たばこ, which comes from Portuguese. See also Transcription into Japanese.
commonly used names of animals and plants, such as トカゲ, ネコ and バラ, and certain other technical and scientific terms, including chemical and mineral names such as カリウム, ポリマー and ベリル.
occasionally, the names of miscellaneous other objects whose kanji are rare, such as ローソク ; the kanji form, 蝋燭, contains the hyōgaiji 蝋.
onomatopoeia, such as ワンワン, and other sound symbolism
emphasis, much like italicisation in European languages.

Katakana can also be used to impart the idea that words are spoken in a foreign or otherwise unusual accent; for example, the speech of a robot.

Rōmaji

The first contact of the Japanese with the Latin alphabet occurred in the 16th century, during the Muromachi period, when they had contact with Portuguese navigators, the first European people to visit the Japanese islands. The earliest Japanese romanization system was based on Portuguese orthography. It was developed around 1548 by a Japanese Catholic named Anjirō.
The Latin alphabet is used to write the following:

Latin-alphabet acronyms and initialisms, such as NATO or UFO
Japanese personal names, corporate brands, and other words intended for international use
foreign names, words, and phrases, often in scholarly contexts
foreign words deliberately rendered to impart a foreign flavour, for instance, in commercial contexts
other Japanized words derived or originated from foreign languages, such as Jリーグ, Tシャツ or B級グルメ
Arabic numerals

s are often used to write numbers in horizontal text, especially when numbering things rather than indicating a quantity, such as telephone numbers, serial numbers and addresses. Arabic numerals were introduced in Japan probably at the same time as the Latin alphabet, in the 16th century during the Muromachi period, the first contact being via Portuguese navigators. These numerals did not originate in Europe, as the Portuguese inherited them during the Arab occupation of the Iberian peninsula.
In the modern period, Japanese keyboards, such as the IME, primarily default their usage to the fullwidth Unicode Arabic numerals as opposed to, though most actual usage uses the common halfwidth one, especially when used to represent a quantity. The fullwidth character may be used for spacing purposes aesthetically.