Help with feature of English?

Question

In the sentence, 'O beautiful dream, why have you disappeared' (words used in a recent mocking text aimed at younger audiences) what feature of English does the 'O' bit at the start of sentence adhere to?

I am aware of why it is used (to emphasis the persons passion on the particular subject), but I need to know what feature this is known as?

Answer 1

May I suggest an aspirational sigh

Ohhhh  [With the languid look of someone lost in reverie]  

Answer 2

It is called an "interjection".  Words like "Oh", "Wow", "Yeah" and others like them all fall into this category.  They will often be followed by an exclamation point, but not always.

Anyone who grew up watching Schoolhouse Rock will instantly know the answer to this question.  In fact, now I can't get the Interjection song from Schoolhouse Rock out of my head. Yow!

Answer 3

I suppose you would say it is an exclaimation.

Answer 4

"O" is the article for the vocative case.  It shows that "beautiful dream" is the name of the thing being directly spoken to.

The thing is, normal contemporary English doesn't distinguish the vocative case.  Older versions of English did, but in modern usage it has dropped completely away.  Vocative case and nominative case are nowadays grammatically indistinguishable.

It does get occasional use in language that tries to sound old-fashioned, such as poetry and religious tracts.

It shouldn't be confused with "oh", which is an interjection.  When it is used, "O" is always capitalized, and always placed just before the object of direct address, and there is no comma placed after it.  "Oh" is only capitalized when at the beginning of a sentence, can be placed almost anywhere, and is always set off with a comma or commas.

"Oh, John, what did you accomplish?" -- "oh" is used to catch John's attention, but it's just an interjection.

"O Jon, what hast thou wrought?" -- "O" to mark Jon as the one being spoken to, along with a bunch of other old-fashioned jargon.

"O" is the vocative article, just as "a" or "an" is the indefinite article and "the" is the definite article.  Technically, that makes it an adjective.