The functional meaning of letters in written speech can be divided into 3 groups: designation of vowel sounds (10), consonants (21), and not designating sounds (2). Most letters are used to denote sounds in a basic, strong position. And the designation of sounds in a changed (weak) position is governed by spelling rules.
The question of the purpose of letters, the expression of a particular sound value, is the main question of the theory of the alphabet. It is known that the letters of the Russian alphabet can be single-digit and two-digit. Sound meanings appear within a syllable. In a word, the relationship between letter and sound meanings is complex. The rules for using letters are divided into 2 categories: the first speaks about the meaning of the letters of the Russian language, regardless of the spelling of certain words (the teachings of L. Shcherba). For example, the statement that the letter "o" has two sound meanings - "o" and "a" - is incorrect. It has only one meaning - "o", and the fact that "o" is written where the sound "a" is sometimes heard is a substitute use of this letter in accordance with the rules of modern spelling. The second category is about writing specific words. According to another famous linguist A. Gvozdev, the letter "o" has a new meaning in the words "big", "dove", "water", etc., which is sound, but not the main (main), but secondary. In this case, the letter "o" remains unambiguous. Consequently, the rules of the first category are the rules of graphics, and the second - the rules of spelling. The use of each letter is limited to a certain sound, which can be found and summed up, although it is sought in specific words, sometimes even at their junction ("The digger was ill - earth / bb / olel.") The definitions of the main (main) and secondary purpose of the letter, proposed by B. Osipov, are the most accurate: the main meaning is the meaning that remains behind the letter, regardless of the spelling rules. The meaning, which is due to spelling rules, is called secondary (additional). The main meanings are inherent in letters in strong positions (vowels under stress, consonants before vowels), the rest are secondary.
