According to the alphabetic principle, letters and combinations of letters are the symbols used to represent the speech sounds of a language based on systematic and predictable relationships between written letters, symbols, and spoken words. The alphabetic principle is the foundation of any alphabetic writing system (such as the English variety of the Roman alphabet, one of the more common types of writing systems in use today). In the education field, it is known as the alphabetic code. Alphabetic writing systems that use an (in principle) almost perfectly phonemic orthography have a single letter (or digraph or, occasionally, trigraph) for each individual phoneme and a one-to-one correspondence between sounds and the letters that represent them, although predictable allophonic alternation is normally not shown. Such systems are used, for example, in the modern languages Serbo-Croatian (arguably, an example of perfect phonemic orthography), Macedonian, Estonian, Finnish, Italian, Romanian, Spanish, Georgian, Hungarian, Turkish, and Esperanto. The best cases have a straightforward spelling system, enabling a writer to predict the spelling of a word given its pronunciation and similarly enabling a reader to predict the pronunciation of a word given its spelling. Ancient languages with such almost perfectly phonemic writing systems include Avestic, Latin, Vedic, and Sanskrit (Devanāgarī—an abugida; see Vyakarana). On the other hand, French and English have a strong difference between sounds and symbols. The alphabetic principle is closely tied to phonics, as it is the systematic relationship between spoken words and their visual representation (letters). The alphabetic principle does not underlie logographic writing systems like Chinese or syllabic writing systems such as Japanese kana. Korean was formerly written partially with Chinese characters, but is now written in the fully alphabetic Hangul system, in which the letters are not written linearly, but arranged in syllabic blocks which resemble Chinese characters. Latin alphabet Most orthographies that use the Latin writing system are imperfectly phonological and diverge from that ideal to a greater or lesser extent. This is because the ancient Romans designed the alphabet specifically for Latin. In the Middle Ages, it was adapted to the Romance languages, the direct descendants of Latin, as well as to the Celtic, Germanic, Baltic, and some Slavic languages, and finally to most of the languages of Europe. English orthography English orthography is based on the alphabetic principle, but the acquisition of sounds and spellings from a variety of languages and differential sound change within English have