Next, the _responsa_ or _auctoritas jurisprudentium_, by which were intended the judicial decisions and the authority of the legal writings of the famous jurisconsults. Imperial rescripts recognized these _responsa_ as authoritative for the Roman courts; and some of the emperors embodied portions of them in formally promulgated collections, thereby giving them the force of law. Justinian’s _Digest_ is the great example of this method of codification.[346] One need scarcely add that the authoritative writings and _responsa_ of the jurisconsults extended and applied the _jus gentium_, that is to say, the rules and principles of the best-considered jurisprudence, freed so far as might be from the formal peculiarities of the _jus civile_ strictly speaking. And the same was true of the praetorian edict. The Roman law also gave legal effect to _inveterata consuetudo_, the law which is sanctioned by custom: “for since the laws bind us because established by the decision of the people, those unwritten customs which the people have approved are binding.”[347] Simply naming the sources of Roman law indicates the ways in which it grew, and the part taken by the jurisconsults in its development as a universal and elastic system. It was due to their labours that legal principles were logically carried out through the mass of enactments and decisions; that is, it was due to their large consideration of the body of existing law, that each novel decision--each case of first impression--should be a true legal deduction, and not a solecism; and that even the new enactments should not create discordant law. And it was due to their labours that as rules of law were called forth, they were stated clearly and in terms of well-nigh universal applicability. The Laws of the Twelve Tables showed the action of legal intelligence and the result of much experience. They sanctioned a large contractual freedom, if within strict forms; they stated broadly the right of testamentary disposition. Many of their provisions, which commonly were but authoritative recognitions, were expressions of basic legal principles, the application of which might be extended to meet the needs of advancing civic life. And through the enlargement of this fundamental collection of law, or deviating from it in accordance with principles which it implicitly embodied, the jurists of the Republic and the first centuries of the Empire formed and developed a body of private and public law from which the jurisprudence of Europe and America has never even sought to free itself.