nsual merely indicates that the Obligation is here
annexed at once to the _Consensus_. The Consensus, or mutual assent of
the parties, is the final and crowning ingredient in the Convention,
and it is the special characteristic of agreements falling under one
of the four heads of Sale, Partnership, Agency, and Hiring, that, as
soon as the assent of the parties has supplied this ingredient, there
is _at once_ a Contract. The Consensus draws with it the Obligation,
performing, in transactions of the sort specified, the exact functions
which are discharged, in the other contracts, by the _Res_ or Thing,
by the _Verba_ stipulationis, and by the _Literae_ or written entry in
a ledger. Consensual is therefore a term which does not involve the
slightest anomaly, but is exactly analogous to Real, Verbal, and
Literal.

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 t