Question

Acquisition by exchange is learned from the verse, “Now this was formerly done in Israel concerning redemption and exchange…”
The verse describes a customary procedure regarding the transfer of ownership.
The Sages derive from this that ownership can be transferred through the legal act of exchange.
There are legal procedures for creating new ownership status—in a sale, in taking possession, and so on.
The Torah directs the process, and there are derivations from verses about how to do this.
The meta-halakhic question is: what is the content of this derivation?
An act of acquisition is conventional: when people want to create changes in the status of an object and the like, they are essentially creating a legal effect, an ideal essence that exists in a legal sense.
In order for us to identify the process in the physical world, we create a process, an act, that symbolizes the legal effect taking place. Thus one could say that the act of acquisition is the manifestation of the legal effect; when the acquisition occurs, that is the sign that a legal effect exists.
A great deal can be analyzed here: is the act of acquisition merely evidentiary, or is it a condition and procedure, a kind of activation button? Either way, there are no inherent laws regarding acquisition, since by its nature it is something conventional.
If so, the question arises: what exactly does the Torah want with the modes of acquisition that it teaches? Why does it need to teach us modes of acquisition? Why does it need to direct us which modes of acquisition to use? It should be enough for us to establish a mode of acquisition and that would be that.
Or perhaps the Torah really did establish legal norms independently of Jewish law?
As for legal effects themselves, seemingly they are something universal. Ownership is a social status; if there were only one person in the world, he could not be an owner, because it would have no meaning. These essences are created because of interactions between people: this is mine because it is not anyone else’s.
Or take the legal effect of marriage: it exists because there is a woman and people determine her legal status.
Now one can ask whether these legal effects also apply to gentiles.
With acquisitions it seems so, but what about betrothal?
Why does a gentile not have betrothal? After all, this is a universal process; it has no halakhic content.
Admittedly, there would be no practical consequences, because a gentile is prohibited regarding another man’s wife only on the factual plane, but on the essential plane there would still be a state of betrothal.
Or should we say that the whole state of betrothal is defined in accordance with its prohibitory consequences, since there is a halakhic definition of a betrothed woman—one who is designated for her husband, permitted to him in sexual relations, and forbidden to the rest of the world. If so, only someone within the halakhic system belongs to the definition of betrothal; someone outside it, like a gentile, has no relevance to betrothal, and therefore it does not exist for him.
Because its entire existence is only in relation to its halakhic consequences.
All a gentile would have is social marriage, not normative marriage.
The question, essentially, is why if two people perform a legal act accepted by everyone, but it is not halakhically defined, they do not acquire. After all, this is something universal; even if the Torah wanted to, it could not prevent ownership.