There are two big reasons for Scotland's retention of its legal system. The first is that the parts that did in fact embrace Roman law were fundamentally opposed in terms of mechanics to that of the courts of England. The second is England in reality has two types of courts, courts of law, and courts of equity (chancery courts), whereas Scotland never made such a distinction.

Tackling the Roman law part requires somewhat of a civics lesson in order to full embrace and understand how it is diametrically opposed to common law. Roman law takes court decisions and codifies them (think quasi statute), but only temporarily because edicts were only the judge's "program for his year in office." ^Source. That eventually changed, but that is a different discussion for a different thread. The common law courts were different in two respects to Roman law in that the court decisions that were made told subsequent courts how they should rule on facts similar to a prior decision (this is different than Roman law because a Roman edict would decide a subsequent case prior to it even making it to court, whereas common law allowed for a more nuanced discussion of the legal issues (think 95% of the facts are similar to a prior case, but the other 5% are what the true legal question is over).

So as you can imagine, the Roman edicts were more like a brute force solution, while common law courts were more like a scalpel only deciding what was necessary to get an outcome that served justice. But, the common law system seems great /u/MasonDixonTexan! Why would Scotland not want to embrace that system?

Since the English system was more narrow, that meant more cases could and would go to court, and get decisions. This meant that England had a lot more, and a lot more comprehensive court made law. That court made law was made by English judges that may have never set foot in Scotland, nor understood Scottish customs. Additionally, while Roman law had a type of precedent, but it was EXTREMELY limited, as noted above, and only lasted for a term in office before it was 'reset.' English court precedent on the other had lasted indefinitely, only being dispensed with either by an Act of Parliament, or a subsequent case made by either the same court that made the original decision (think level of court, not the judge personally) or a higher court dispensed with it. To put things in perspective, common law precedents can last a long time, decades, or even hundreds of years. Bringing back to English made law being forced onto Scottish people; imagine a one hundred year old English case dictating the outcome of your Scottish case, made by an outsider? It is possibly outdated, and culturally/legally out of touch. The Scottish courts had to either perpetually reaffirm prior decisions, which would subject court decisions to the times, or drop them. To some, that is a benefit.

The second point delves into the issue of the English court structure. The English system had two types of courts, courts of law, and courts of equity. Depending on the REMEDY, not the legal issue, that one was seeking, determined which court a plaintiff would bring suit under. If you wanted money damages, you went to a court of law. If you wanted anything else besides money, you generally went to a court of equity. Usually those remedies would consist of things like, specific performance (compelling a party to fulfill their contractual obligations - which is generally unfavored, unless necessary), estoppel (when someone is promised something either explicitly or implicitly and unduly relies on that promise to their own detriment), and others were used here. Scotland made no such distinction, their judges had functionally equivalent remedial powers of both a law and equity judge in England. If Scotland took this route, and embraced the English system, it would divest its judges of long held powers, for what would have been seen as an arbitrary reason. It would then require that more judges be brought on, and thus cost more money.

When you understand the legal systems at issue themselves, in conjunction with the cultural differences of the two countries, it becomes clear why Scotland ardently retained this portion of its identity.

Hope this helps!

Your question implies that (a) Scotland had a civil law system, (b) which was based on Roman law, and (c) which was retained after the Union.

Whether any of these claims are true is debatable.

There was an indigenous Scots law which was influenced by Roman law as Scottish lawyers started to study law in universities in France (and after Reformation in the Netherlands). As Evans-Jones puts it: ‘Roman law was taught in the universities but not applied in the courts. Indigenous law was applied in the courts but not studied in the universities. The reception is the process by which “Roman law”, which was studied in the universities, supplanted indigenous law in the courts as the law of the land.’^(1)

Evans-Jones opines that Scots law was essentially an uncodified civil law system until the 19th century, when English law came to be seen as something attractive and it was embraced. He considers that the reception of foreign legal ideas ‘happen when strong legal systems come up against weak legal systems. The strong system, to a greater or lesser extent, then overwhelms the weak system. Quite contrary to the popular image that Scots private law is the product of “critical choosing” the manner in which this “overwhelming” has occurred in Scotland has usually been fairly indiscriminate. When the resulting body of law is a “mixture” it is often worse than the alternatives from which it is drawn.’^(2)

English law

On the other hand, Sellar (and number of other academics) argues that Scots law has always been a ‘mixed’ system, influenced by both the English common law and the civilian law. There was an early borrowing from Anglo-Norman law during the reign of David I to Bruce (1124-1329). This included, for example, the introduction of justiciars, sheriffs, the office of the Chancellor, and the granting of land on feudal land tenure.^(3) (For more on this period, see the Paradox of Medieval Scotland.) Sellar is of the opinion that this borrowing did not come to a sudden end, but continued, which, he says, shows that ‘the model for the emerging Scottish common law was undoubtedly the Common Law of England, to such a degree that it is legitimate, I believe, to speak of a Reception.’^(4)

Sellar's view is that Scots law was always influenced by English law, which can be measured in three ways: first, the continuing legacy of the Scoto-Norman law (the ‘first reception’); secondly, further occasional direct borrowing from England; thirdly, the views of contemporary writers on the relationship between Scots and English law (e.g. Thomas Craig). One of the most important Scottish legal texts, Stair’s Institutions of the Law of Scotland (1681), when referring to ‘our ancient customs’, in fact, lists several examples based on English common law.^(5)

Roman law

The ‘reception’ of Roman law was different. The first ‘reception’, according to Evans-Jones, took place in the twelfth century through Canon law (but it was confined mainly to procedural matters) while the second, and perhaps the most important, reception was ‘the systematic and extensive use of Roman law during the seventeenth and eighteenth centuries in the creation of a system of private law.’^(8) Civil law (ius commune), including Roman law, was used widely in legal argument throughout the seventeenth and eighteenth century, e.g. in Burnet v Burnet [1701] Mor 2284 in which references were made to, inter alia, the Corpus Juris Civilis, Bartolus, Cujacius, and the opinion of a ‘Cornelius Van Eck, the famous professor of law presently at Utrecht’.^(9)

Roman law, however, has never been considered to be an authoritative source of law.^(10) Thomas Craig in 1603 wrote that ‘We, in this kingdom, are bound by the laws of the Romans to the extent that they agree with the laws of nature and correct reasoning (…)’.^(11) Viscount Stair was influenced heavily by Roman law, but wrote that ‘though it be not acknowledged as a law binding for its authority, yet, being, as a rule, followed for its equi^(t)y.’6 (He also borrowed heavily from Thomas Craig and Continental writers, such as Grotius, Vinnius, and Gudelinus.^(7)) Different areas of law have been influenced by Roman law to different extent but none is based entirely on Roman law. That is not to say that Roman law was not an important influence (in fact it continues to be cited in courts occasionally). As Sellar puts it: ‘Reception of Roman law affected not only the vocabulary but also the very grammar of Scots law.^(’1)2 Canon law, before the Reformation, was also a major influence. (Stein is of the view that ‘before 1400 the main influence of Roman law on Scots law was exerted through the medium of canon law rather than directly.’)^13

Union

The Treaty of Union preserved ‘Laws which concern private Right, except for evident Utility of the Subjects within Scotland’. It also guaranteed the existence ‘in all time coming’ of the Court of Session, High Court of Justiciary, the ‘anicent universities’, and the Church of Scotland. There was much less commitment to the preservation of the Scottish legal system, universities and church after the Union.^(14) The House of Lords (sitting as the highest appeal court) decided in Greenshields v Magistrates of Edinburgh in 1709 that it had jurisdiction to hear appeals from the Court of Session. (It did not hear appeals from criminal cases however.) The decision to allow an episcopal minister to conduct services in Edinburgh went against the Treaty of Union (and the judgment eventually ‘created an environment that led to the Disruption of 1843’).^(15)

While superficial changes were made, ‘the basic architecture of Scottish legal institutions continued intact’ mainly due to legislative neglect.^(16) Important changes were made to commercial law to ease cross-border commerce, following the developments in English law.^(17) Commercial law continued to be developed with a unified British code in mind (e.g. Sale of Goods Act 1893 or the Companies Acts)^(.1)8 A number of other areas of law, however, remained independent and ‘continued to develop on its own principles’ (e.g. Scots criminal law which is fairly distinct from the criminal law in the rest of the U^(K)).19

Nevertheless, as noted above, from the 19th century the influence of civil tradition diminished and the citation of English cases became quite a common occurrence.^(20) Cairns states that the change started earlier, around 1750, when the reliance on civil law and Roman sources started to decline.^(21) There was also a move towards legal unity resulting in Scots law losing many of its civilian characteristics.^(22) Evans-Jones explains it as follows: ‘Sitting as the highest court of appeal for both jurisdictions, on a number of occasions during this century, the House of Lords has actively sought to create a unitary law, or to achieve similar results, for both Scottish and English private law. The normal practice is that Scots law is made to conform with the law of England, even where the principles of its law would not naturally lead to such a result.’^(23) (The role of the House of Lords, and that of the Supreme Court, has been sometimes controversial.)

Since the late Victorian period there has been a renewed focus on Scots law which became even more pronounced since devolution (resulting sometimes in a push against the influence of English law). Cairns concludes that ‘despite the assimilation of much English practice and doctrine, Scots law nonetheless remained different from English law because of its civilian heritage derived from the jus commune.’^(24)