is concentrated. Such a mental engagement, signified through external
acts, the Romans called a Pact or Convention; and when the Convention
has once been conceived as the nucleus of a Contract, it soon becomes
the tendency of advancing jurisprudence to break away the external
shell of form and ceremony. Forms are thenceforward only retained so
far as they are guarantees of authenticity, and securities for
caution and deliberation. The idea of a Contract is fully developed,
or, to employ the Roman phrase, Contracts are absorbed in Pacts.

The history of this course of change in Roman law is exceedingly
instructive. At the earliest dawn of the jurisprudence, the term in
use for a Contract was one which is very familiar to the students of
historical Latinity. It was _nexum_, and the parties to the contract
were said to be _nexi_, expressions which must be carefully attended
to on account of the singular durableness of the metaphor on which
they are founded. The notion that persons under a contractual
engagement are connected together by a strong _bond_ or _chain_,
continued till the last to influence the Roman jurisprudence of
Contract; and flowing thence it has mixed itself with modern ideas.
What then was involved in this nexum or bond? A definition which has
descended to us from one of the Latin antiquarians describes _nexum_
as _omne quod geritur per aes et libram_, "every transaction with the
copper and the balance," and these words have occasioned a good deal
of perplexity. The copper and the balance are the well-known
accompaniments of the Mancipation, the ancient solemnity described in
a former chapter, by which the right of ownership in the highest form
of Roman Property was transferred from one person to another.
Mancipation was a _conveyance_, and hence has arisen the difficulty,
for the definition thus cited appears to confound Contracts and
Conveyances, which in the philosophy of jurisprudence are not simply
kept apart, but are actually opposed to each other. The _jus in re_,
right _in rem_, right "availing against all the world," or Proprietary
Right, is sharply distinguished by the analyst of mature jurisprudence
from the _jus ad rem_, right _in personam_, right "availing a single
individual or group," or obligation. Now Conveyances transfer
Proprietary Rights, Contracts create Obligations--how then can the two
be included under the same name or same general conception? This, like
many similar embarrassmen