(Edward S. Klima)
Of course, all writing systems are arbitrary to some extent, but the arbitrariness is minimal if orthographic units are correlated with the elements of the linguistic structure -- linguistic elements that the language user already knows just by the fact that he knows the language. (...) Having learned the sound forms of the words of the language -- which are themselves in essence arbitrary with respect to their meaning -- he would then have to associate with these as many arbitrary sequences of letters. Such system of writing does not capitalize on a structural characteristic of every human language, namely, that the sound forms of the thousands of words in each are all made up of a limited number of distinctive sounds. Thus there is a reduction of arbitrariness when letters, while themselves arbitrary, have a fixed relationship to the form of the word. (...)
If orthography provides a visual representation of an utterance (words, expressions, phrases), then an orthography is not sufficiently expressive if two words, which have different inherent sound forms, do not differ in their orthographic representation. We shall assume that an optimal orthography would not tolerate a situation like that in English where read (present tense) and read (past tense) or lead (meaning 'to conduct') and lead (the metal) have a different sound-form but have the same orthographic representation. Our consideration of the expressive power of a writing system need not necessarily be restricted to the sound form of the word, to the exclusion of other levels of language. Consider, for example, the general phenomena of homophony -- when two different lexical items have the same sound forms: bill 'a demand for a payment' versus bill 'the break of a bird'; meat 'flesh of an animal' versus meet 'a gathering'. The orthography is more expressive of the language if it distinguishes these forms, while identical at the sound-level, are distinct at the lexical-level. With such a distinction the orthography would be more expressive than the language is at the sound level.