222 HARVARD LAW REVIEW. allowed to enrich himself unjustly at the expense of another, it is also true that no acts whereby one does so unjustly enrich himself at the expense of another are allowed by law, or to state the propo- sition conversely, all such acts are by law forbidden. The proposi- tion may therefore be stated in this form : Acts whereby one unjustly enriches himself at the expense of another are forbidden by law. Now that which the law forbids is illegal. The very definition of illegality is the quality or condition of being in contravention of law. Our proposition may therefore undergo another transforma- tion and, still with no change of sense, become : Acts whereby one unjustly enriches himself at the expense of another are illegal. In this proposition the verb " enriches " states the doing of an act while the adverb " unjustly" qualifies it by stating the mode of the doing. To state the same act by a noun and to qualify it by the corresponding adjective is a common substitution and involves no change of meaning. To make such a substitution in the present case will give the proposition this form : Acts of unjust ejirichment of one at the expense of another are illegal. But acts <?/ unjust en- richment are acts resulting in unjust enrichment and if the act is illegal, so is the result. Indeed it is almost tautological to say "acts of unjust enrichment," for an unjust enrichment is itself an act. The proposition may then be reduced to its lowest terms as follows: The tmjttst e?irichment of one at the expense of another is illegal. It is extremely unlikely that the exact identity of this proposition with the proposition as enunciated by the author would be disputed, for it is apparent on the face of the matter; but I have been thus particular in setting out the various transpositions in order to avoid the possibility of error. The proposition as it now stands is in the normal form of a juridical principle, in which the subject should define a general class of acts and the predicate should define their juridical quality. Now it is to be noted that in the present form, as well as in all the transmutations, the word
- unjust" is of the essence. It is not true that a man may not en-
rich himself at another's expense, because that he may, legally and rightfully and intentionally. Thus it requires no authority to prove that an innocent purchaser for value may enforce against the maker a promissory note which after the purchase he learns to have been procured by fraud and imposition. That is enriching himself at the expense of the maker, but the enrichment is neither unlawful nor unjust. It is necessary, therefore, to consider the meaning of this word unjust.
