What part of speech is ago? [duplicate]
Four score and seven years ago, our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.
sbj: fathers
det: our
vrb: brought forth
obj: nation
det: a
adj: new
adj: *conceived*
adv: <in>
obj: liberty
cnj: and
adj: *dedicated*
adv: <to>
obj: proposition
det: the
adj: -that-
sbj: men
det: all
vrb: are created
cmp: equal
adv: <on>
obj: continent
det: this
adv: ...?
I'm working on this but can't wrap my head around the phrase in bold. I know that it's adverbial phrase of time, but what kind of phrase is it exactly? What part of speech is 'ago'? Sources don't seem to agree.
Solution 1:
"ago" in its current form is a preposition of time, as it describes the relationship between two nouns: the current time and a past event. "Four score and seven years ago" is therefore an adverb prepositional phrase, with the object being the noun phrase "four score and seven years" and the preposition being "ago".
Solution 2:
It is a good question, but the function word "ago" does not fit into one of the traditional word classes. The important thing is to understand that "ago" derives from the past participle "agone", a compound verb of to go meaning to pass.
"ten years ago" was "ten years have gone/agone". So this explains why "ago", which functions like a preposition, is placed after the noun group it is connected to.
There are a lot of terms as to the word class of ago. But they don't explain much. It is necessary to understand the origin of ago.