Appeal is a grammatically independent word or phrase, which calls the interlocutor or the addressee of speech, formed with the help of a special ringing intonation.
As a rule, the appeal is expressed by the nominative case of the noun (less often – by other nominal parts of speech), both with dependent words (common circulation), and without them (unspoken). It can stand anywhere in the sentence, it is not any member of the sentence and is separated from other words by commas. Appeal may be a separate proposal, issued at the end of the exclamation mark. For example: My friend, my motherland, we will devote our souls to wonderful impulses! (AS Pushkin); How terrible to us with you, comrade my big one! (OE Mandelstam); Old man! I heard many times that you saved me from death (M. Yu. Lermontov).
In some cases, forms that do not coincide with the nominative are used as references. It can be like the remnants of the old sacrificial case that existed in the Old Russian language (like friends, elder, father, God, Lord), and truncated forms that coincide with the basis, typical for colloquial speech (such as moms, Wan, Mash, etc. .). For example: Give me, Lord, give me a sign that I have understood Thy will (NS Gumilev); A fish came to him and asked: “What do you need, older?” (AS Pushkin); You, Zin, are rushing to rudeness, everything, Zin, you are trying to offend (VS Vysotsky).
Appeal may be accompanied by particles o (the most common particle), but (appears usually when repeating word forms), ah, etc. Oh baby, I cried for a long time over your fate (SA Yesenin); Mom, and Mom, what should I do now? Ah Nadia, Nadia, I would be for a twenty-dollar one in any direction of your soul! (B. Sh. Okudzhava).