Orthographic depth

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. In other words, 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. Such examples include Spanish, Italian, Finnish, and Turkish.

Esperanto, being an artificial language, was made to be the most transparent as possible, with one letter - one phoneme fixed relation.

In contrast, in deep (opaque) orthographies, the relationship is less direct, and the reader must learn the arbitrary or unusual pronunciations of irregular words. In other words, deep orthographies are writing systems that do not have a one-to-one correspondence between sounds (phonemes) and the letters (graphemes) that represent them. They may be irregular (English), reflect etymology (Hungarian, Faroese or French) or be morphophonemic (Korean).

Written Korean represents an interesting hybrid; each phoneme in the language is represented by a letter but the letters are packaged into "square" units of two to four phonemes, each square representing a syllable. Korean is not completely shallow but has some exceptions in which the written word is not pronounced exactly as the individual letter-phoneme correspondences would otherwise require. English has many such instances: compare the pronunciation of the letter "c" in the words "magic" and "magician" or the pronunciation of the letter "i" in "pint" and "mint".

According to the orthographic depth hypothesis, shallow orthographies are more easily able to support a word recognition process that involves the language phonology. In contrast, deep orthographies encourage a reader to process printed words by referring to their morphology via the printed word's visual-orthographic structure. For languages with relatively deep orthographies such as English, French, Arabic or Hebrew, new readers have much more difficulty learning to decode words. As a result, children learn to read more slowly. For languages with relatively shallow orthographies, such as Italian and Finnish, new readers have few problems learning to decode words. As a result, children learn to read relatively quickly.

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