One may suspect that religious obligation arising from the detention of property is a legal way of putting it in a polity in which social control is primarily religious and religious precepts are turning into legal precepts. At any rate the Hindus carry the idea of religious obligation so far that a descendant is bound to pay the debts of his ancestor in many cases whether he receives any assets of the ancestor or not. The liability of the son to pay the father's debt is held to arise from the moral and religious duty of rescuing the father from the penalties attaching in a future state to non-payment of debts. Accordingly if the debt is of such a kind that no penalties would so attach, there is no religious duty and hence no obligation imposed upon the descendant. Roman law in its earliest stage was not unlike this. Agreements of themselves were not cognizable by the tribunals. It was no ground for summoning a defendant before the magistrate that he had made a promise and had broken it. Agreements were matters for religion or for kin or guild discipline. If one had called on the gods to witness his promise or sworn to fulfil it, he was liable to pontifical discipline. The presence of an impious oath breaker was a social danger and he might be devoted to the infernal gods. As law replaced religion as the controlling regulative agency, the old religiously sanctioned promise becomes a formal legal contract. Thus in the strict law we get formal contracts with their historical origin in religious duty, and formal contracts with their historical origin in a legal duty created by a real transaction of suretyship or conveyance, perhaps by calling the people to witness so that there is an affront to the state if they are called upon in vain. When contact with Greek philosophers set the Roman jurists to thinking about the basis of obligation, there were two sorts of promises: (1) Formal promises, (a) by stipulation, using the sacramental word _spondeo_ and thus assuming the pouring out of a libation that the gods might take notice of the promise, (b) by public ceremony apparently symbolizing a real transaction before the whole people, (c) entered upon the household books of account, and (2) mere informal promises not recognized by law. The latter depended wholly on the good faith of the maker since the law had put down self-help which formerly had been available to the promisee. Accordingly Roman jurists distinguished civil obligations and natural obligations--those recognized and secured legally and those which primarily had only a moral efficacy. A _nudum pactum_ or mere agreement or mere promise, not clothed with legal efficacy because it did not come within any of the categories of legal transactions sanctioned by the _ius ciuile_, created only a natural obligation. It was right and just to adhere to such a pact, but only contracts, undertakings recognized by law because of their form or nature, were enforceable.