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. 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 Hindi, Spanish, Finnish, Turkish, Latin and Italian. 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 reflect etymology (English, Faroese, Mongolian script, Thai, French, or Franco-Provençal) or be morphophonemic (Korean or Russian). Written Korean represents an unusual 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 has very complex phonological variation rules, especially regarding the consonants rather than the vowels, in contrast to English. For example, the Korean word 훗일, which should be pronounced as [husil] based on standard pronunciations of the components of the grapheme, is actually pronounced as [hunnil]. Among the consonants of the Korean language, only one is always pronounced exactly as it is written. Italian offers clear examples of differential directionality in depth.