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 embarrassments, has been occasioned by the error of ascribing to the mental condition of an unformed society a faculty which pre-eminently belongs to an advanced stage of intellectual development, the faculty of distinguishing in speculation ideas which are blended in practice. We have indications not to be mistaken of a state of social affairs in which Conveyances and Contracts were practically confounded; nor did the discrepance of the conceptions become perceptible till men had begun to adopt a distinct practice in contracting and conveying.
It may here be observed that we know enough of ancient Roman law to give some idea of the mode of transformation followed by legal conceptions and by legal phraseology in the infancy of Jurisprudence. The change which they undergo appear to be a change from general to special; or, as we might otherwise express it, the ancient conceptions and the ancient terms are subjected to a process of gradual specialisation. An ancient legal conception corresponds not to one but to several modern conceptions. An ancient technical expression serves to indicate a variety of things which in modern law have separate names allotted to them. If however we take up the history of Jurisprudence at the next stage, we find that the subordinate conceptions have gradually disengaged themselves and that the old general names are giving way to special appellations. The old general conception is not obliterated, but it has ceased to cover more than one or a few of the notions which it first included. So too the old technical name remains, but it discharges only one of the functions which it once performed. We may exemplify this phenomenon in various ways. Patriarchal Power of all sorts appears, for instance, to have been once conceived as identical in character, and it was doubtless distinguished by one name. The Power exercised by the ancestor was the same whether it was exercised over the family or the material property -- over flocks, herds, slaves, children, or wife. We cannot be absolutely certain of its old Roman name, but there is very strong reason for believing, from the number of expressions indicating shades of the notion of power into which the word manus enter, that the ancient general term was manus. But, when Roman law has advanced a little, both the name and the idea have become specialised.
Power is discriminated, both in word and in conception, according to the object over which it is exerted. Exercised over material commodities or slaves, it has become dominium -- over children, it is Potestas -- over free persons whose services have been made away to another by their own ancestor, it is mancipium -- over a wife, it is still manus. The old word, it will be perceived, has not altogether fallen into desuetude, but is confined to one very special exercise of the authority it had formerly denoted. This example will enable us to comprehend the nature of the historical alliance between Contracts and Conveyances. There seems to have been one solemn ceremonial at first for all solemn transactions, and its name at Rome appears to have been nexum. Precisely the same forms which were in use when a conveyance of property was effected seem to have been employed in the making of a contract.
But we have not very far to move onwards before we come to a period at which the notion of a Contract has disengaged itself from the notion of a Conveyance. A double change has thus taken place. The transaction "with the copper and the balance," when intended to have for its office the transfer of property, is known by the new and special name of Mancipation. The ancient Nexum still designates the same ceremony, but only when it is employed for the special purpose of solemnising a contract.
When two or three legal conceptions are spoken of as anciently blended in one, it is not intended to imply that some one of the included notions may not be older than the others, or, when those other have been formed, may not greatly predominate over and take precedence over them. The reason why one legal conception continues so long to cover several conceptions, and one technical phrase to do instead of several, is doubtless that practical changes are accomplished in the law of primitive societies long before men see occasion to notice or name them.
