I happen to be teaching classes on both The Lord of the Rings and Aquinas’s economic theory at the moment, so you’ll understand why this stuff is on my mind.
In my recent post on the hobbits’ not-so-positive attitude towards possessions, I noted the passage in which Frodo had a “tussle with young Sancho Proudfoot (old Odo Proudfoot’s grandson), who had begun an excavation in the larger pantry, where he thought there was an echo. The legend of Bilbo’s gold excited both curiosity and hope; for legendary gold (mysteriously obtained, if not positively ill-gotten) is, as every one knows, any one’s for the finding–unless the search is interrupted.”
Contrary to Tolkien’s narrator, however, it’s not quite true that “every one knows” that legendary gold is free for the finding and taking. According to Aquinas, for example,
With regard to treasure-trove a distinction must be made. For some there are that were never in anyone’s possession, for instance precious stones and jewels, found on the seashore, and such the finder is allowed to keep [*Dig. I, viii, De divis. rerum: Inst. II, i, De rerum divis.]. The same applies to treasure hidden underground long since and belonging to no man, except that according to civil law the finder is bound to give half to the owner of the land, if the treasure trove be in the land of another person [*Inst. II, i, 39: Cod. X, xv, De Thesauris]. Hence in the parable of the Gospel (Matt. 13:44) it is said of the finder of the treasure hidden in a field that he bought the field, as though he purposed thus to acquire the right of possessing the whole treasure. On the other Land the treasure-trove may be nearly in someone’s possession: and then if anyone take it with the intention, not of keeping it but of returning it to the owner who does not look upon such things as unappropriated, he is not guilty of theft. In like manner if the thing found appears to be unappropriated, and if the finder believes it to be so, although he keep it, he does not commit a theft [*Inst. II, i, 47]. In any other case the sin of theft is committed [*Dig. XLI, i, De acquirend. rerum dominio, 9: Inst. II, i, 48]: wherefore Augustine says in a homily (Serm. clxxviii; De Verb. Apost.): “If thou hast found a thing and not returned it, thou hast stolen it” (Dig. xiv, 5, can. Si quid invenisti). (ST II-II.66.5, ad 2)
So there you go: even if young Sancho had found some treasure hidden in Frodo’s larger pantry, according to Aquinas, it would not have been his “for the finding,” but theft (but then you already knew that, didn’t you?).