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 naturalised 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 (or range of meanings), 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 few if any native speakers know anywhere near this number. 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 (that is, each different syllable, strictly each mora) 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 are logographic characters (based on traditional ones) taken from Chinese script and used in the writing of Japanese.