In the intercourse of life the commonest and most important of all the contracts are unquestionably the four styled Consensual. The larger part of the collective existence of every community is consumed in transactions of buying and selling, of letting and hiring, of alliances between men for purposes of business, of delegation of business from one man to another; and this is no doubt the consideration which led the Romans, as it has led most societies, to relieve these transactions from technical incumbrance, to abstain as much as possible from clogging the most efficient springs of social movement. Such motives were not of course confined to Rome, and the commerce of the Romans with their neighbours must have given them abundant opportunities for observing that the contracts before us tended everywhere to become Consensual, obligatory on the mere signification of mutual assent. Hence, following their usual practice, they distinguished these contracts as contracts Juris Gentium. Yet I do not think that they were so named at a very early period. The first notions of a Jus Gentium may have been deposited in the minds of the Roman lawyers long before the appointment of a Praetor Peregrinus, but it would only be through extensive and regular trade that they would be familiarised with the contractual system of other Italian communities, and such a trade would scarcely attain considerable proportions before Italy had been thoroughly pacified, and the supremacy of Rome conclusively assured. Although, however, there is strong probability that the Consensual Contracts were the latest-born into the Roman system, and though it is likely that the qualification, Juris Gentium, stamps the recency of their origin, yet this very expression, which attributes them to the "Law of Nations," has in modern times produced the notion of their extreme antiquity. For, when the "Law of Nations" had been converted into the "Law of Nature," it seemed to be implied that the Consensual Contracts were the type of the agreements most congenial to the natural state; and hence arose the singular belief that the younger the civilisation, the simpler must be its forms of contract.
The Consensual Contracts, it will be observed, were extremely limited in number. But it cannot be doubted that they constituted the stage in the history of Contract-law from which all modern conceptions of contract took their start. The motion of the will which constitutes agreement was now completely insulated, and became the subject of separate contemplation; forms were entirely eliminated from the notion of contract, and external acts were only regarded as symbols of the internal act of volition. The Consensual Contracts had, moreover, been classed in the Jus Gentium, and it was not long before this classification drew with it the inference that they were the species of agreement which represented the engagements approved of by Nature and included in her code. This point once reached, we are prepared for several celebrated doctrines and distinctions of the Roman lawyers. One of them is the distinction between Natural and Civil Obligations.
When a person of full intellectual maturity had deliberately bound himself by an engagement, he was said to be under a natural obligation, even though he had omitted some necessary formality, and even though through some technical impediment he was devoid of the formal capacity for making a valid contract. The law (and this is what the distinction implies) would not enforce the obligation, but it did not absolutely refuse to recognise it; and natural obligations differed in many respects from obligations which were merely null and void, more particularly in the circumstance that they could be civilly confirmed, if the capacity for contract were subsequently acquired. Another very peculiar doctrine of the jurisconsults could not have had its origin earlier than the period at which the Convention was severed from the technical ingredients of Contract. They taught that though nothing but a Contract could be the foundation of an action, a mere Pact or Convention could be the basis of a plea.
It followed from this, that though nobody could sue upon an agreement which he had not taken the precaution to mature into a Contract by complying with the proper forms, nevertheless a claim arising out of a valid contract could be rebutted by proving a counter agreement which had never got beyond the state of a simple convention. An action for the recovery of a debt could be met by showing a mere informal agreement to waive or postpone the payment.
The doctrine just stated indicates the hesitation of the Praetors in making their advances towards the greatest of their innovations. Their theory of Natural law must have led them to look with especial favour on the Consensual Contracts and on those Pacts or Conventions of which the Consensual Contracts were only particular instances; but they did not at once venture on extending to all Conventions the liberty of the Consensual Contracts. They took advantage of that special superintendence over procedure which had been confided to them since the first beginnings of Roman law, and, while they still declined to permit a suit to be launched which was not based on a formal contract, they gave full play to their new theory of agreement in directing the ulterior stages of the proceeding. But, when they had proceeded thus far, it was inevitable that they should proceed farther. The revolution of the ancient law of Contract was consummated when the Praetor of some one year announced in his Edict that he would grant equitable actions upon Pacts which had never been matured at all into Contracts, provided only that the Pacts in question had been founded on a consideration (causa).
