Verb 'aim' and usage

Dear Mo2men,
That's a great question. I'm happy to respond.

In some ways, we are getting into the metaphorical, almost poetic, side of language. These are issues that will not appear much on the GMAT SC.

The sentences in which "aim" is used as a verb are perfectly correct:
1) The agreement among countries aims at unifying them.
2) The agreement among countries aims to unifying them.
These are grammatically and idiomatically correct. They can and do appear in newspapers and news journals this way. In a way, though, we are being metaphorical here, because really it's the people who write the treaty or negotiate the treaty that have intentions and aims. The treaty itself is really a piece of paper with no mind of its own. In a stark literal sense, we can't say that the treaty "aims" anything. Here, we are being a little metaphorical: insofar as the treaty represents the aggregate of the intentions, the aims, of a large number of people, we can say that the treaty "aims" to do something. Because this is metaphorical, almost personifying a document, this cuts some corners with logic, as poetry often does and should. That's fine, and it's perfectly acceptable in popular news reporting, but such liberal use of metaphor is less common in more academic writing, and GMAT leans toward this less metaphorical and more literal side. Conceivably, #1 or #2 could still appear on the GMAT.
If we were going to be hyper-literal, we would say
3) The agreement among countries is aimed at at unifying them.
That's also correct, and technically, this is logically correct now, but it's a little longer, and taking a longer way to specify something that is already well understood in a commonly used metaphor makes this sound a little stodgy and stilted. What fuddy-duddy would say #3?

Now, suppose we have a participle. Remember that the present participle, "aiming," is an active participle, and the past participle, "aimed," is a past participle. Hence, if we are going use a participle construction, the grammar forces us to make a logical choice between active & passive construction. In particular, with the same number of words, we could choose the active or the passive construction. Well, if it is not going to take one syllable more to say this in the logically correct fashion, then the metaphor loses a great deal of its utility. It is logically correct to say that the treaty is an object of its authors' aiming and that it doesn't do any aiming on its own. Thus, we use the past participle, the passive participle.
4) The agreement aimed at unifying the countries has not been finalized.
We would be far less likely to see:
5) The agreement aiming at unifying the countries has not been finalized.
Yes, this does continue the metaphor we had in #1 and #2, but the only true advantage of the metaphor in #1 and #2 was that it created a brevity and sense of clarity & directness that #3 lacked. It made sense to use the metaphor if we could communicate meaning more quickly. Well, once we use the participle construction, sticking with the metaphor doesn't help us anymore: it has lost its principal advantage and utility.

If poetry & metaphor are a more concise way to communicate meaning, then why use the overwordy literal phrasing? But once conditions change, and it just as concise and just as direct to say what we have to say either metaphorically or literally, then utility of metaphor declines significantly. Now, admittedly, in poetry, in song lyrics, in humorous banter, etc. there are many other values to metaphor, but the cut-and-dry factual world of the GMAT, metaphor is on an extremely short leash.

All this is quite sophisticated and beyond what most folks would need to understand for the GMAT SC.

Does all this make sense?
Mike