Although the Estonian orthography is generally guided by phonemic principles, with each grapheme corresponding to one phoneme, there are some historical and morphological deviations from this: for example preservation of the morpheme in declension of the word (writing b, g, d in places where p, k, t is pronounced) and in the use of 'i' and 'j'.[clarification needed] Where it is very impractical or impossible to type š and ž, they are substituted with sh and zh in some written texts, although this is considered incorrect. Otherwise, the h in sh represents a voiceless glottal fricative, as in Pasha (pas-ha); this also applies to some foreign names.

What principles usually govern the Estonian orthography?