What was an Obligation? It is defined by the Roman lawyers as "Juris vinculum, quo necessitate adstringimur alicujus solvendae rei." This definition connects the Obligation with the Nexum through the common metaphor on which they are founded, and shows us with much clearness the pedigree of a peculiar conception. The Obligation is the "bond" or "chain" with which the law joins together persons or groups of persons, in consequence of certain voluntary acts. The acts which have the effect of attracting an Obligation are chiefly those classed under the heads of Contract and Delict, of Agreement and Wrong; but a variety of other acts have a similar consequence which are not capable of being comprised in an exact classification. It is to be remarked, however, that the act does not draw to itself the Obligation in consequence of any moral necessity; it is the law which annexes it in the plenitude of its power, a point the more necessary to be noted, because a different doctrine has sometimes been propounded by modern interpreters of the Civil Law who had moral or metaphysical theories of their own to support. The image of a _vinculum juris_ colours and pervades every part of the Roman law of Contract and Delict. The law bound the parties together, and the _chain_ could only be undone by the process called _solutio_, an expression still figurative, to which our word "payment" is only occasionally and incidentally equivalent. The consistency with which the figurative image was allowed to present itself, explains an otherwise puzzling peculiarity of Roman legal phraseology, the fact that "Obligation" signified rights as well as duties, the right, for example, to have a debt paid as well as the duty of paying it. The Romans kept in fact the entire picture of the "legal chain" before their eyes, and regarded one end of it no more and no less than the other.