A minimally professionalized lawyer-advocate is less of an independent agent with interests diverging from those of their appointers. This, in a nutshell, is the image I depicted in three previous posts. If each member of society contemplates needing to defend themselves and their associates in court, they would think differently of rights, laws, and justice. (Free-speech-happy men and women would likely pause before they claim and exercise their constitutional rights, left and right.) I would have been satisfied to stop here, but my material did open a can of worms, and I can’t put the worms back in. (Just as Pandora lost control over what came out of her jar—that jar that became a box; hence, Pandora’s box not Pandora’s jar; one more line of inquiry for fun.) This last post addresses the observed similarity displayed in Roman and Islamic law throughout the texts I employed in these three posts.
WHY ARE DIFFERENT LEGAL SYSTEMS SIMILAR?
In the area of slave laws, Islamic law is more or less an improvement on Roman law. Muslim jurists simply took what was there and ameliorated it. Muslim jurists, for instance, would free a concubine who bore a child for her master upon the master’s death and prohibited her sale (she would be called umm walad), just as Roman lawyers would allow such a female slave to become free after she bore her master three children. Roman lawyers considered these three children to be slaves, while subsequent children were born free. The latter doctrine led to a somewhat amusing quandary in Roman law addressing what to do with a female slave who bore one child then a triplet; whether the last of the triplet was, or was not, free.
In other areas, the similarity is simply a function of good legal reasoning at work. Both Roman and Muslim jurists employed a version of this principle: Laws cease, when the causes for which they were instituted change. Muslim jurists speak of intifā’ al-ḥukm li intifā’ sababih—“laws are moot whose reasons are moot.” Roman jurists articulated a similar principle: cessante ratione legis, cessat et ipsa lex, which would sound something like this in English: “The law ceases (or is vacuous), when its cause ceases (or is vacated).” Historians of Roman law spoke of a dispute among the jurists as to whether every instance of the disappearance of a legal cause makes the law fully moot; an uncertainty that was transferred to the European legal traditions. Oxford Romanist H. F. Jolowics believed this rule could only be identified in the writings of the medieval glossators—medieval commentators on the Digest—(hence subsequent to early Islamic jurisprudence), as opposed to its pre-Islamic tradition. Regardless of who stated it first, it is on the books of both Roman and Islamic law.
Then there are doctrines that follow certain social organizations. The Digest’s treatment of praedial (land-related) servitudes (Book 8, Servitudes) finds a clear equivalent in medieval Islamic law in ḥuqūq al-irtifāq, that is, rights attached to properties, such as homes and land, including access to the main road, water, and shared passages, and drainage systems.Within discussions of the general doctrines, such as these praedial servitudes, one also finds similarity in concepts and doctrines. For example, Ḥanafī jurists hesitate to consider a “utility” (or manfa‘a), such as access to a home, a type of concrete property (māl). (They, a bit circuitously, say it becomes such—it becomes a subject of contract—once it is included in a contract, hence when you rent an apartment, the utility of residing in it and using it becomes a type of property.) In Digest 8, 1, 14, prelude, Paul is quoted as saying:
PAUL, Sabinus, book 15: Rustic praedial servitudes, even though attached to corporeal property, are nevertheless incorporeal and so are never acquired by usucapion. Or the reason may be that the nature of these servitudes is such as not to engender clear and continuous possession.For no one can make use of a right of way in so continuous and uninterrupted a manner that his possession of it will be held to be unbroken. The same rule applies to urban praedial servitudes as well (emphasis added).
The Ḥanafī doctrine that old lawsuits may not be heard, after 15 years, in some cases, or 33 years in others, also invoke Roman laws’ imposition of an expiry date on some claims. The more broadly accepted legal maxim “No judge ought to rule on another’s rulings”—al-ijtihād la yunqaḍbi-l-ijtihād echoes Digest 45, 1, 6:
6 PAUL, Edict, book 70: It has been accepted for good reason that in individual disputes a single action and one final judgment is sufficient, lest otherwise the ambit of suits be greatly increased and cause very great and insurmountable difficulty, especially if different judgments were pronounced. To be subject to a defense of res judicata is therefore frequent (emphasis added).
Similarity, I hope historians don’t still think, correspondence is to be found only when two systems are focused on one and the same question. That is to say, similarity will not be limited to the same doctrine occurring exactly in the same area of law in two regimes (say, the laws of partnership, or the rights of neighbors). Consider the following instance. The laws of tithes, in Canon law, state that a transfer of chattel carries with it all that belongs with that chattel, unless otherwise is explicitly stipulated in the transfer. In Ḥanbalī law, when a chattel is usurped, its natural progeny must be returned to settle the usurpation. (A case analogous to this does confuse readers who assume that an element of usury is included here; so, when I take over your apartment for a year, on Ḥanbalī law, I must return with it the revenue expected from its rental, or use, based on the same principle; the payment for use is seen as the same as a cow’s milk and calf; that is, it is not usurious).
The point is that one may not only look for similarities in areas where two legal regimes tackle the very same question. You can see how daunting an attempt to study similarities within such a broad scope would be. In any case, establishing and denying similarities, let alone influence, is a possibility one may accept but not get fixated on, especially for ideological and/or religious purposes.
Similarities between laws, finally, is not limited to ideas and practices such as legal representation and urban or rustic space planning. They come, in some cases, in little puzzling details and nuances. For instance, something like a fixation on a number, as an indicator of a quality. Every one of us will be vigilant to note that a concept originating in Latin will not be the same in Arabic. Terms and concepts can never be universal. But how about numbers? Applied, say, to age? What if two different legal conventions take age 25 to indicate that a person of that age reached a degree of maturity and, on that basis, can be assigned legal consequences upon reaching that age? One may still argue that the populations are different. One may say that 25 years in Palestine in the 2nd century is not the same as 25 years in 8th century Iraq. This is certainly true. But it may only be trivially true, and it may be an inviting riddle to contemplate, when we find this number assigned to reaching majority travelling centuries from a Latin text in 6th century Constantinople (originating, in fact, from earlier texts and legal edicts) to an Arabic text in 8th Iraq and then again to a Castilian text in 13thcentury Spain, and finally to a 19th century Ottoman-Turkish text and many 20th and 21st century legal texts, including ones in Danish and Italian.
Take the following text in Justinian’s Digest (D, 4, 4, 1, 1-3), where Ulpian, the noted Levantine Roman jurist (d. 223), discussed a pretorian edict regarding individuals under age 25 (after a chapter on “Malice and Fraud”):
The Praetor says in the Edict: “With respect to what is alleged to have been done by a person under twenty-five, I shall treat the case as the circumstances demand.” 2. It is evident that he offers help to those under twenty-five. For it is agreed that after this age the strength of a full-grown man is reached. 3. And, therefore, today, up to this age, young men are governed by curators and under this age the administration of their own property should not be entrusted to them, even though they might be able to look after their own affairs well (emphasis added).
A few centuries later, you will note that Abū Ḥanīfa (d. 150/767) ruled out interdiction procedures (hajr) against those 25 years or older, wondering whether a mature man who fathered could be subjected to interdiction by his own children. Was Iraq’s Kufa in the 7th and 8th centuries under the influence of a prejudice that originated in the mind of Roman praetors from the 2nd century? Possibly. Equally plausible is that there is a lot more. Be that as it may, the mysterious, arbitrary appeal to age 25 in both traditions remains worthy of investigation. In 13th century Spain, Alfonso X’s (“The Wise” d. 1284) Libro des la Leyes or the Siete Partidas (“the Seven Books of Law”) remains committed to the age 25 as the age when one reaches adulthood. The 1876 Ottoman Constitution made 25 the age threshold required for voting; Denmark set 25 as the age of voting before 1953; Italy, still today, requires its citizens to be 25 to vote in senate elections.
How a scholar treats similarities between ideas and practices shows her or his intellectual bandwidth. A naive post hoc, ergo prompter hoc (“it came before, hence it was a cause”) line of reasoning bespeaks narrow horizons and limited imagination. It is a sure way to undermine any and all productive studies of the coincidences of similarity and dissimilarity across legal institutions. Normally a scholar would hesitate, further investigate, or suspend judgment altogether until clear lines of meaning for the similarities reveal themselves. In most cases, it is advisable to juxtapose similar materials and leave it up to further research efforts to explain and clarify the observed affinities.
You and I must be thinking that sundry, lost data are needed for us to be fully certain of the nature of the transfer of ideas and practices from one end to the other. (When data is available, there are other problems, including the quality of the sources and their indeterminacy, walls separating academic fields, etc.) It might still not be easy to know how transfers of ideas happened. In the case of early Islamic law, one must note the obvious first: Muslims were in charge; they were more powerful than the Roman, Jewish, Syrian, and Zoroastrian populations whose ideas and practices they may have appropriated, after modification, to serve purposes known or unknown to these populations.
I hope itis not only, like beauty, in the eye of the beholder. We may remember that W. W. Buckland, for example, found many institutions in the common law and Roman law to be similar. However, he tended to see more similarity among older institutions of different traditions than even between legal ancestors (e.g., Roman law) and their modern legal scions (the modern European civil law tradition). He states: “[I]t seems to be the truth that there is more affinity between the Roman jurist and the common lawyer than there is between the Roman jurist and his modern civilian successor.” Modern Romanists (the so-called pandectists) invented a logico-legal structure unknown to either Roman or common law jurisprudence, Buckland insists.
Following this line of reasoning, one would need to retract a juxtaposition of ancient laws with modern Ottoman, Danish, and Italian laws’ fixing legal maturity, for certain purposes, around age 25. But my point is less ambitious than Buckland’s. The point is that many solutions to recurring social problems will look similar. There is no good explanation for that. Every society can accept or remove parts of its (social, moral, and legal) heritage. But it seems to go back to some simple questions and with them accept similar answers.
When considering similarity, one must also consider cases where a principle is reversed. The Qur’ān specifies a sixth of the inheritance as a share to be given to a maternal (enate) brother of the deceased. The maternal brother is deprived of inheritance in Roman law. It is still true that Roman law (and common law and Islamic law) prefer the male line in inheritance. But it is also the case that the Qur’ān here seems to solve a problem that existed in Roman (and Arabian society), namely the exclusion of very close relatives (maternal brothers) from inheritance. This solution led to its own problems, as historians of Islamic law know, since guaranteeing a maternal (enate) brother a share in the inheritance while asking full (cognate) brothers to wait for the remainder of the inheritance (to collect all of it as male agnates) led to the strange conclusion that brothers sharing a mother with the deceased may get more than brothers who share both mother and father, a problem the second caliph, ʿUmar b. al-Khaṭṭāb (d. 23/644) was credited with solving. ʿUmar allowed the full brothers to share the inheritance with the maternal brothers of the deceased.
My short answer to the question “Why are there similarities and overlaps among different legal regimes?’” is that I don’t know. Nor, in many cases, do others. If need is the mother of (scientific) invention, so it (need) can lead different minds to picking similar solutions to similar problems. It could be that different societies faced similar needs. It could be the case that one inherited answers from another, picked out a few and discarded the rest, then left some intact. And it could be many other things.
Notes to part 4:
 H.F. Jolowics, The Roman Foundation of Modern Law 15-16 (1957).
 Digest 8, 1, 14, prelude.
 In Digest (44, 1, 3), Gaius speaks to the opposite rule: that some lawsuits may be allowed only after the passage of a certain period—under temporary and dilatory defenses. “Temporary and dilatory defenses are those which are not available at any time, but can be avoided, such as the defense of the temporary agreed pact, that is, that no action shall be brought within, say, five years; defenses affecting a procurator are also dilatory, and they can be avoided.”
 An issue I discussed in detail in a 1997 study. See Ahmad Atif Ahmad, Istiʼnāf al-aḥkām al-qaḍāʼīyah wa-naqḍuhā fī al-tashrīʻ al-Islāmī : maʻa al-muqāranah bi-al-tashrīʻāt al-waḍʻīyah (1997). No English translation is available.
 Digest 45, 1, 6.
 Richard Helmholz, Canon Law and Roman Law, inThe Cambridge Companion to Roman Law 413 (David Johnston ed., 2015). Helmholz notes that the calf is also a burden, for canonists, not a mere product of the cow; their argument, in a sense, is more complex, as it carries the logic of “with benefits come burdens.” The similarity remains: Products are a part of their source, when property and rights are calculated and exacted.
 D, 4, 4, 1, 1-3.
 M.b.H. Shaybānī, Al-Mabsut/Al-Asl vol. VIII, at 476(Qatar Religious Endowments Ministry/Ibn Hazm Publications ed. 2012) (c. 804-805) (on interdiction/hajr).
 What was going on before the Muslim conquests is also a question of some difficulty and significance in understanding and explaining what Muslims allowed and didn’t allow after the conquests. According to Uriel Simonsohn, exempting non-Zoroastrians from laws regulating Zoroastrians in areas such as inheritance law, for example, was the practice of pre-Islamic Zoroastrian governments. See Uriel I. Simonsohn, A Common Justice: The Legal Allegiances of Christians and Jews under Early Islam 49 (2011) (quoting a ruling from the case-law book The Book of Thousand Judgments to the effect that non-Zoroastrians didn’t need to appoint a successor to the deceased and then speculating as to why that was).
 W.W. Buckland & Arnold D. McNair, Roman Law and Common Law: A Comparison in Outline xvi (F. H. Lawson rev., Cambridge Univ. Press 2nd ed. 1952).