Phrases like 100 years ago from when? and Our honeymoon was ten years ago from next Tuesday seem to be viable, interestingly.
That statement suggests doubt about whether the subject phrases are viable. They certainly are viable, but their internal construction is not clear.
Generally (the prime exception being cases of fronting), a PP modifies or complements a preceding phrase, which usually is the nearest preceding VP or an intervening NP. As examples: In will play on the beach of my youth, the PP of my youth adjectivally modifies the NP the beach. In will play on the beach next week, the PP next week adverbially modifies the VP will play.
In ten years ago next Tuesday, we have an interesting syntactic puzzle. There are two PPs. The first is headed by the post-positional ago, and the second is headed conventionally by next. Without the latter PP, it would be clear that the complement of ago is ten years.
How is this phrase structured? Does the PP next Tuesday look beyond the intervening preposition, ago, to adjectivally modify the NP ten years? Does the PP next Tuesday adverbially modify the entirety of the PP ten years ago? Or is there some better analysis?
A semantic analysis is somewhat revealing. The phrase describes a point in time that occurs ten years prior to the Tuesday immediately following the point in time at which the phrase is stated. We understand the preposition ago as being an instruction to count backwards in time. We understand the NP ten years as telling us how far back to count. Normally, ago implies that the counting should start from now, the present day. Here, we understand next Tuesday as specifying a different point in time from which to begin counting.
It seems clear that the phrase next Tuesday does not modify the duration ten years. That sort of modification would be non-sensical. Similarly, next Tuesday cannot properly be understood to modify the concept of the point in time that happens to be ten years prior to now. That leaves the possibility that next Tuesday modifies the preposition ago.
The semantics of the phrase suggest that the preposition ago takes two arguments, one argument that specifies the starting point for counting and the other argument, usually implied to be now, that specifies how far back to count. However, our traditional model of PPs allows for only one argument (the complement of the PP), not two arguments--except when a PP is pre-modified by an adverbial.
PPs can be modified by adverbials. Take, for instance, nearly in the soup. Based on semantics, the AdvP nearly does not seem to modify the NP the soup. Rather, it seems to modify either the entirety of the PP in the soup or solely the preposition in. My sense of the meaning is that nearly changes the meaning of in before in acts upon its complement the soup. This suggests in is taking two arguments.
So it seems that nearly acts as an adverbial adjunct to the preposition in. In parallel, perhaps it is valid to analyze the NP next Tuesday as functioning as an adverbial adjunct to the preposition ago.
On this basis, I argue that prepositions are capable of taking two arguments. One argument is the usual prepositional phrase complement that imbues the preposition with substance. The other argument, an optional argument, can modify the meaning of the preposition itself.
In the case of nearly in, the meaning of in takes on a distinct change. It no longer means in. It means something like, not in but in an area that is close to being in. Similarly, in the case of ago next Tuesday, the meaning of ago is changed. It no longer is ago measured from the implicit now. It is ago measured from an explicit next Tuesday. That modified form of ago is what then acts upon the complement ten years.
Thus, ten years ago next Tuesday essentially has the same structure as nearly in the soup, but the sequence of the members of the structure are reversed: Complement-Preposition-Adjunct vs. Adjunct-Preposition-Complement. Perhaps, when dealing with a post-positional, that sort of inversion can be expected and may even be necessary. Absent the preposition intervening between the complement and the adjunct, the phrase might be quite difficult to parse.
That takes me full circle to the sentence in the title of this post: Our nation declared independence 246 years ago tomorrow. I believe tomorrow modifies the preposition ago.
While I am sure papers must exist on this subject, I have not yet found one. Any suggestions or comments would be appreciated.