But, even apart from the adoption of legal standards, Roman law exercised a notable influence upon the legal thought of the new intruders into a country whose jurists had been trained in the scientific jurisprudence of the school of Berytus. The influence exercised by the Roman legal methods on the system of legal deduction in Islam is a more important factor in the history of Moslem civilisation than even the direct adoption of particular points of law. By what systematic rules or what devices can deductions be drawn from positive laws, written or traditional, which shall apply to newly arising cases at law and to the decision of legal questions for which the positive written law provides no answer? In dealing with this juridical problem the Arab Fukha took their stand entirely upon the instruction they had gained from circles familiar with the work of Rome in the domain of law. The dualism of written law (Arabic, nazz) and unwritten law is a mere reflection of the dualism of leges scriptæ (chakhamim), and leges non scriptæ. Just so, about half a century before, the Jewish jurists (a word which in its legal application is likewise a translation of the Roman term jurisprudentes) had been moved by their intercourse with the Romans to make the hitherto unrecognised distinction between the tora she-bitche-thab, or written law, and the tora she-be’al-peh, or oral law.
The application of principles and rules borrowed from the methodology of Roman jurisprudence first made it possible to extend the limited legal material supplied by the Koran and the old decisions which were accepted as the basis of the law, to other departments of juridical activity, of which these authorities had had no prevision. The ratio legis (illa), the principle of presumption was applied to analogies (kyas) in words and things; nay, just as Roman legal practice gave great weight to the opinio prudentium in legal deduction, so the Islamite prudentes assumed the prerogative of an authoritative subjective opinio; for ra’j, as it is called in Arabic, is a literal translation of the Latin term. Of all these principles (which are not exhausted by the examples just cited) none more strikingly demonstrates the profound influence of Roman law on the development of legal opinion in Islam, than that which is known in Arabic as maclaha or istilah,—i.e., the public weal and regard for the same. The significance of this principle lies in the license it grants to the interpreter of the law to apply the legal standard in the manner best fitted to serve the public weal and interests. Here we recognise the Roman standard of the utilitas publica, which gives the interpreter of the law the right, by interpretation, an application to wrest a plain and unambiguous law into something quite different from its original meaning, in the interests of the public weal.
Such principles, derived from foreign instructors, served for the deduction of Mohammedan law, as soon as the teachers of the people felt the necessity of withdrawing the domain of law from the capricious action of the sovereign and his instruments in the administration and judicature, which had free play by reason of the meagreness of positive legal matter based upon generally recognised authority. The Islamite jurists declared that the conclusions at which they had arrived on the basis of these principles (which, as we have seen, were no part of Islam) were in harmony with the true spirit of Islam, the rightful outcome of its original character. This phenomenon, which early came to maturity and was widely accepted in Mohammedan theological circles as legal and of indubitable authority, is of profound importance to our historic estimate and judgment of Islam. Whatever the ignorant men who stood by its cradle may have thought to be the meaning of the new word which they were charged to proclaim to the oriental world, the first step which conquering Islam took on its victorious career taught it to accommodate itself to an alien spirit, and to mould its own intellectual heritage by influences which seem absolutely heterogeneous to a superficial observer.
In more than one point of its doctrinal fabric, Islam in its early days was a borrower. Its founders were anxious, it is true, to avoid the appearance of appropriating other men’s property. But loudly as they trumpet the principle, “Be different from them in all things” (Chalifuhum) the reference here being chiefly to Jews and Christians, their documents are crammed with borrowings from the Scriptures of the very confessions which, on their own assertion, it was their leading principle to oppose. The stubborn antagonism of Islam to the rest of the world, its inflexible protest against the influence of foreign elements, is an illusion which historical study of the movement must dissipate if it is to rise to a scientific comprehension of this great historic phenomenon.
Though contact with the Romæi was the influence which caused the first seeds of law in Islam to germinate, we must not overlook another side upon which Islam in its early days came into direct contact with a foreign national element, the influence of which was very important in the development of its legal system. We refer to its contact with the people and the religion of Persia. This can be traced back to pre-Islamite times, and even Mohammed himself was not absolutely free from the influence of the religious ideas of the Parsees (madjus, magians), whom he classes in the Koran with Jews and Christians, and contrasts with the heathen as confessors of more favoured religions.
But Persian nationality did not become a formative element in Islam until the latter subjugated the geographical sphere of the old Parsee religion, and by the right of conquest imposed the faith of the prophet of Mecca and Medina upon the followers of Zoroaster. The Mohammedan occupation of ’Irak is one of the most telling factors in the religious and juridical development of Islam.