O is also used as an ejaculation expressive of a wish or desire, when it is joined to the following clause by the word for or that.
O for rest and peace !
that I had wings like a dove !
As an interjection expressing surprise, indignation, or regret, O is frequently followed by an implied ellipsis and the word that.
O [it is sad] that I should live to see this day!
O is common as an exclamation in trivial speech : as, O my ! O dear ! In many Southern States O is the customary beginning of familiar and abrupt address, as O John! O James!
Oh, an ejaculation evoked by pain or woe, or by sudden emotion, as surprise, consternation, or delight, properly takes a lower-case letter (except when beginning a sentence), and is followed by an exclamation-point either directly after the oh or at the end of the exclamatory phrase.
But she is in her grave, and oh !
The difference to me !
Oh, how I suffer !
Oh ! my offence is rank, it smells to heaven.
Oh is often used, even in the Northern States, as a colloquial introduction to a sentence, as in
Oh, James, I am glad to see you.
Oh, yes, it is quite satisfactory.
