Orthographic depth

The orthographic depth of an alphabetic orthography indicates the degree to which a written language deviates from simple one-to-one letter–phoneme correspondence. It depends on how easy it is to predict the pronunciation of a word based on its spelling: shallow orthographies are easy to pronounce based on the written word, and deep orthographies are difficult to pronounce based on how they are written.

In shallow orthographies, the spelling-sound correspondence is direct: from the rules of pronunciation, one is able to pronounce the word correctly. That is to say, shallow (transparent) orthographies, also called phonemic orthographies, have a one-to-one relationship between its graphemes and phonemes, and the spelling of words is very consistent. Examples include Japanese kana, Hindi, Lao (since 1975), Spanish, Finnish, Turkish, Georgian, Latin, Italian, Serbo-Croatian, Ukrainian, and Welsh.

In contrast, in deep (opaque) orthographies, the relationship is less direct, and the reader must learn the arbitrary or unusual pronunciations of irregular words. Deep orthographies are writing systems that do not have a consistent one-to-one correspondence between sounds (phonemes) and the letters or characters (graphemes) that represent them. Instead, spellings tend to reflect etymology (whether real or perceived) and/or historic pronunciation. Examples include English, Danish, Swedish, Faroese, Chinese, Tibetan, Mongolian, Thai, Khmer, Burmese, Lao (until 1975; now only used overseas), French, and Franco-Provençal.

Orthographies such as those of German, Hungarian (mainly phonemic with the exception ly, j representing the same sound, but consonant and vowel length are not always accurate and various spellings reflect etymology, not pronunciation), Portuguese, modern Greek, Icelandic, Korean, Tamil, and Russian are considered to be of intermediate depth as they include many morphophonemic features.