It is generally conceded, and it is undoubtedly true, that the forum of the law is not of equal jurisdiction with the forum of the conscience, and that some acts may be ethically unjust which are yet permissible in law. Unjust acts may be therefore either unjust and legal or unjust and illegal. This difference may be indicated in our proposition, which will then take on either of these two forms:—
1. The unjust and legal enrichment of one at the expense of another is illegal.
2. The unjust and illegal enrichment of one at the expense of another is illegal.
In the first of these two propositions, if it be laid down as a principle of jurisprudence, the law is made to characterize the act according to its standards in one way in the subject, that is, to declare it legal, and to characterize the same act by the same standards in a contradictory way in the predicate, that is, to declare it illegal. The word "unjust" does not in any way relieve the conflict between subject and predicate, and may therefore be neglected. The first proposition then reduces itself to a contradiction in terms.
The second proposition is obviously true. An illegal enrichment is of course illegal. Such a proposition, however, subserves no useful purpose. It is like the equation in mathematics, A = A, from which no deduction can be drawn, being in truth only a seeming equation. There are not in fact two objects which are equated, because the apparent equation means only that the thing equals itself, that is, there is only one object of contemplation. Such a proposition is entitled in logic an identical proposition and is recognized as true, but also as logically valueless. It is a truism, rather than a truth.
The proposition, therefore, with which the learned author began, No one shall be allowed to enrich himself unjustly at the expense of another, reduces itself according to the interpretation of the word "unjustly," either to a contradiction in terms or else to a mere identical proposition, and in either case cannot ever be a true principle of jurisprudence. The first form of the proposition, being a contradiction in terms, self-evidently cannot become such a principle. The second is equally valueless, but for the different reason that no conclusion can ever be drawn from an identical proposition. This can be demonstrated in the present instance if an attempt is made to use the proposition as a guiding principle or reason of deciding any particular concrete case.
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