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which has descended to us from one of the Latin antiquarians describes nexum as omne quod geritur per æs 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 preeminently belongs to an advanced stage of intellectual development, the faculty of distinguishing in speculation ideas which are blended in practice.