bit of private magic employed to conjure up legal liability. It was the clothing in legally recognized vestments of an intention to do what reason and good faith demand in a given situation. When form and intention concurred the promisor must answer for what he undertook. When the form used did not express or went beyond the intention or was the product of an apparent but not a real intention, the promisee was not to be enriched unjustly at the promisor's expense on the sole basis of the form. Moreover the duty was to be one of doing what good faith demanded, not one of doing literally and exactly what the letter of the undertaking called for. And although there was no express undertaking, there might be duties implied in the relation or situation or transaction, viewed as one of good faith, and one might be held to a standard of action because an upright and diligent man, who was his own master, would so act. Such is the mode of thinking in the classical period of the Roman law and it is closely paralleled by an independent development of juristic thought in the rise of equity and the absorption of the law merchant in our law. It was easy to fit the two categories, delict and formal undertaking, which had come down from the strict law, into the new mode of thought. The typical delict required _dolus_--intentional aggression upon the personality or the substance of another. Indeed Aquilian _culpa_, in which the fault did not extend to intentional aggression, is a juristic equitable development. Hence when the legal was identified with the moral, and such identification is a prime characteristic of this stage, the significant thing in delict seemed to be the moral duty to repair an injury caused by wilful aggression. The legal precept was _alienum non laedere_. Also the duty to perform an intentional undertaking seemed to rest on the inherent moral quality of a promise that made it intrinsically binding on an upright man. The legal precept was _suum cuique tribuere_. Thus liability seemed to flow from intentional action--whether in the form of aggression or in the form of agreement. The "natural" sources of liability were delict and contract. Everything else was assimilated to one or the other of them. Liability without fault was quasi-delictal. Liability imposed by good faith to prevent unjust enrichment was quasi-contractual. The central idea had become one of the demands of good faith in view of intentional action.