雖然Rule of Law與憲法有密切的關係，但Rule of Law並不是一個憲法用詞，而是一個憲法原則。作為哲學和政治學概念，Rule of law的基本含義是法治，以別於人治。[2] 在此意義上， Rule of Law與a rule of law, rules of law, rule by law以及rule under law沒有相同之處。無論是a rule of law還是rules of law都應當是指法律原則或法律規定。雖然相近，但Rule of Law並不是a rule of law或rules of law的同義詞。[3] 而rule by law及rule under law雖然相互間存在比較大的一致性，但與rule of law還是有比較明顯的區別。前者中的rule應當是指「統治」或「治理」，而後者中的rule雖有「統治」和「治理」的含義，但顯然並不局限於此。
Rule of Law作為一個哲學和政治學的概念，其基本含義在西方已經有相當長的歷史了。亞里斯多德在他的Politics中就曾提到過法治優於人治的觀點，他說：[4]
… it is more proper that law should govern than any one of the citizens…
馬庫斯·圖留斯·西塞羅 (Marcus Tullius Cicero) 也說過：[5]
We are in bondage to the law in order that we may be set free.
約翰·洛克 (John Locke) 雖然沒有直接使用Rule of Law，但對其含義作出過解釋，他說：[6]
Whoever has the legislative or supreme power in any commonwealth, therefore, is bound (1) to govern by established standing laws, promulgated and known to the people (and not by on-the-spot decrees), with unbiased and upright judges appointed to apply those laws in deciding controversies; and (2) to employ the force of the community at home only in the enforcement of such laws, or abroad to prevent or correct foreign injuries and secure the community from attack.
Rule of Law的含義並非一成不變，隨著時間的推移不斷發生著變化，而且至今沒有形成統一的定義。因此有人把Rule of Law視為自相矛盾的概念：[7]
The concept of the 「rule of law」 is paradoxical. In a literal sense it requires us to be prisoners of an impersonal authority and subject to unpleasant consequences if we transgress… On the other hand the rule of law is often regarded as a liberal, and indeed as liberating idea.
討論Rule of Law恐怕無法不提艾爾伯特·維恩·戴西 (Albert Venn Dicey)，這是因為Rule of Law的現代意義來自於他。[8] 在Introduction to the Study of the Law of the Constitution一書中，戴西對Rule of Law進行了描述。戴西認為rule of law有三個含義：
It means, in the first place, the absolute supremacy or predominance of regular law as opposed to the influence of arbitrary power, and excludes the existence of arbitrariness, of prerogative, or even of wide discretionary authority on the part of the government…; a man may with us be punished for a breach of law, but he can be punished for nothing else.
It means, again, equality before the law, or the equal subjection of all classes to the ordinary law of the land administered by the ordinary Law Courts; the 「rule of law」 in this sense excludes the idea of any exemption of officials or others from the duty of obedience to the law which governs other citizens or from the jurisdiction of the ordinary tribunals…
The 「rule of law,」 lastly, may be used as a formula for expressing the fact that with us the law of the constitution, the rules which in foreign countries naturally form part of a constitutional code, are not the source but the consequence of the rights of individuals, as defined and enforced by the Courts; that, in short, the principles of private law have with us been by the action of the Courts and Parliament so extended as to determine the position of the Crown and of its servants; thus the constitution is the result of the ordinary law of the land.
戴西對Rule of Law作出的描述對之後人們理解Rule of Law不僅產生了深遠的影響，而且還引起了相當大的誤解，始終是爭議的焦點。[12]
弗裡德裡希·奧古斯特·馮·哈耶克 (Friedrich August von Hayek) 也對Rule of Law表示出極大的興趣，但在哈耶克眼中，Rule of Law只是一個政治理想，是自由政治秩序的基石。作為自有資本主義的捍衛者，哈耶克主張的Rule of Law似乎已不再是一個憲法概念了，而是一個更具政治學含義的概念。哈耶克認為Rule of Law並不僅僅要求合法和憲政主義，還應當解決政府行為合法性的問題。[13] 在The Road to Sterfdom一書中這樣寫到：[14]
Nothing distinguishes more clearly a free country from a country under arbitrary government than the observance in the former of the great principles known as the Rule of Law. Stripped of technicalities this means that government in all its actions is bound by rules fixed and announced beforehand – rules that make it possible to foresee with fair certainty how the authority will use its coercive powers in given circumstances and to plan one’s individual affairs on the basis of this knowledge. Thus, within the known rules of the game, the individual is free to pursue his personal ends, certain that the powers of government will not be used deliberately to frustrate his efforts.
在Decline of Rule of Law一文中，哈耶克將Rule of Law與一般的法律條文或規定進行了比較，他這樣寫到：[15]
Since this Rule of Law is a rule for the legislator, a rule about what the law ought to be, it can, of course, never be a rule of the positive law of any land. The legislator can never effectively limit his own powers. The rule is rather a meta-legal principle which can operate only through its action on public opinion. So long as it is generally believed in, it will keep legislation within the bounds of the Rule of Law. Once it ceases to be accepted or understood by public opinion, soon the law itself will be in conflict with the Rule of Law.
2006年11月，託馬斯·賓漢大法官 (Lord Bingham) 在劍橋大學作了題為Rule of Law的演講，他在演講中對Rule of Law的含義進行了進一步的闡述並總結出八個含義。這八個含義分別是：一，法律必須是可知的、易懂的、明確的和可預料的；二，法律權利義務問題應當通過法律適用而不是自由裁量得到解決；三，除非存在客觀差異，法律應當平等適用於所有人；四，法律必須充分保障基本人權；五，必須提供經濟且快速的手段解決當事人無法解決的善意民事糾紛；六，各級政府官員必須行使被合理且善意賦予的權力但不能越權；七，司法程序必須公平；八，現有Rule of Law原則要求政府履行國際法義務。[16] 賓漢對Rule of Law的解釋無疑更傾向於法律的解釋，而保障基本人權、司法程序公平以及政府履行國際法義務無疑帶著當代的烙印。
世界正義工程 (World Justice Project) 使用了一套完全不同的方法衡量了不同國家的法律體系，對Rule of Law進行了闡述並總結出四項原則來：[17]
As used by the World Justice Project, the rule of law refers to a rules-based system in which the following four universal principles are upheld:
· The government and its officials and agents are accountable under the law.
· The laws are clear, publicized, stable, and fair, and protect fundamental rights, including the security of persons and property.
· The process by which the laws are enacted, administered, and enforced is accessible, fair, and efficient.
· Access to justice is provided by competent, independent, and ethical adjudicators, attorneys or representatives, and judicial officers who are of sufficient number, have adequate resources, and reflect the makeup of the communities they serve.
如果Rule of Law是以一項憲法原則為人所知曉的話，世界正義工程對Rule of Law做出的上述解釋明顯帶有國際性，而要在國際範圍內適用憲法原則恐怕是比較困難的。
Rule of Law譯成中文通常是「法治」，但兩者是否具有對應的關係則取決於中文「法治」的真正含義。管仲曰「威不兩錯，政不二門，以法治國，則舉措而已」。[18] 君權不能由兩家佔有，政令不能由兩家制定，因此這裡的「以法治國」不過是一切都按君主的意志來處理而已。韓非子在《有度》中對管仲的思想進行了總結，他說：「威不貳錯，制不共門。威、制共，則眾邪彰矣；法不信，則君行危矣；刑不斷，則邪不勝矣。」但是，無論是管仲的以法治國，還是韓非子的以法治國，與今天的「依法治國」有著本質的區別。「以法治國」的是指其實還是人治。在中國古代，法律的制定是為了維護至高無上的皇權。
《中國大百科全書》把「法治」解釋為依據法律治理國家，是與人治相對的概念。[19]《現代漢語詞典》對「法治」作出了兩個解釋，一個用作名詞，另一個用作動詞。用作名詞是特指先秦時期法家的政治思想，主張以法為準則，統治人民，處理國事。用作動詞時則是指根據法律治理國家和社會。[20] 由此可見，雖然Rule of Law包含了「法治」或「以法治國」的含義，但Rule of Law應當並不僅僅是指法治或依法治國。《辭海》也有「法治」的解釋：[21]
法治與「人治」相對。按照法律治理國家的政治主張。在中國，戰國時法家大力提倡，韓非集法家學說之大成，把法治和術治、勢治相結合，形成體統的法治理論，明確提出「依法治國」、「以法為本」、「治強生於法」、「刑過不避大臣，賞善不遺匹夫」等觀點。古希臘亞里斯多德在《政治學》一書中論述了法治勝於人治，認為「法治應包含兩重意義：已成立的法律獲得普遍的服從，而大家服從的法律又應該本身是制定得良好的法律」。資產階級啟蒙思想家也倡導法治，主張法律面前人人平等，反對任何組織和個人享有法律之外的特權。現代社會的法治則更強調法律與所在社會的互動、個人與社會的和諧、人類與自然的和諧。
根據上述分析，Rule of Law和「法治」並不是一回事。雖然很難在中文中找到含義相同的詞，但把Rule of Law譯成中文的「法治」即使算不上誤譯，至少是不夠妥帖的。相比之下，把rule by law或rule under law譯成「法治」則可能會好不少。
Rule of Law除了作為憲法原則理解外還可以作為a rule of law來理解。1891年出版的A Dictionary of Law，即Black’s Law Dictionary的第一版就對Rule of Law作出了這樣的解釋：[22]
A legal principle, of general application, sanctioned by the recognition of authorities, and usually expressed in the form of a maxim or logical proposition. Called a 「rule,」 because in doubtful or unforeseen cases it is a guide or norm for their decision.
在2009年第9版Black’s Law Dictionary中，Rule of Law共有五條解釋：[23]
1. A substantive legal principle…
2. The supremacy of regular as opposed to arbitrary power…
3. The doctrine that every person is subject to the ordinary law within the jurisdiction…
4. The doctrine that general constitutional principles are the result of judicial decisions determining the rights of private individuals in the courts…
5. Loosely, a legal ruling; a ruling on a point of law…
在上述各條解釋中，只有第二個和第四個解釋可以理解是對Rule of Law作出了哲學或政治學的解釋，其餘的三個解釋都把Rule of Law作為法律原則進行解釋的，即Rule of Law和a rule of law被等同了。我們顯然不能將這三個解釋中的Rule of Law譯成中文的「法治」。
討論憲法與行政法的Constitutional and Administrative Law一書區分了Rule of Law的兩種用法： [24]
The rule of law may be interpreted either as a philosophy or political theory which lays down fundamental requirements for law, or as a procedural device by which those with power rule under the law.
雖然Rule of Law具有類似a rule of law的含義，但通常不是指一條有明確文字或含義的法律原則，而往往是指法律格言或箴言。
在Rule of Law作為a rule of law使用時顯然是無法譯成中文的「法治」或「依法治國」的，下文便是一個例子：[25]
The master and crews are in each case his servants, the freighter in each case is usually without any representative on board the ship; the same opportunities for fraud or collusion occur; and the same difficulty in discovering the truth as to what has taken place arises. Whether the rule of law is wise, or not, it appears to apply as properly to the one class of cases as to the other.
下文中的Rule of Law同樣不能譯成中文的「法治」或「依法治國」：[26]
There is no rule of law that 『time lost』 clauses and laytime clauses constitute two independent and unrelated codes for computing the amount of permitted laytime that has been used up. In the words of Lord Diplock, 『the vessel is to be treated as if during that period she were in fact in berth and at the disposition of the charterer for carrying out the loading or discharging operation ... and ... in the computation of time lost in waiting for a berth there are to be excluded all periods which would have been left out in the computation of permitted laytime used up if the vessel had actually been in berth』.
下文中的Rule of Law同樣不能譯成中文的「法治」或「依法治國」：[27]
Those who uphold and gain from unjust arrangements, and who deny with contempt the rights and liberties of others, are not likely, it is said, to let scruples concerning the rule of law interfere with their interests in particular cases.
[1] The Constitutional Reform Act, 2005, s.1.
[2] 這裡所用「法治」兩字雖有中文的部分含義，但並不與中文含義完全相同。
[3] 應當注意的是，Rule of Law作為哲學和政治學概念與a rule of law沒有相同含義。
[4] Aristotle, Politics Book I, Chapter XVI.
[5] www.123HelpMe.com/view.asp?id=22692, 2 July 2017.
[6] John Locke, Second Treatise of Government, 2 July 2017.
[7] John Alder, General Principles of Constitutional and Administrative Law, 4th edition, Palgrave, 2002, p.92.
[8] Colin Turpin et al, British Government and the Constitution, 6th edition, Cambridge University Press, 2007, p.40; A.W. Bradley et al, Constitutional and Administrative Law, 14th edition, Pearson Education 2007, p.96.
[9] A.V. Dicey, Introduction to the Study of the Law of the Constitution, 5th edition, Macmillan & Co Ltd, 1897, p.193.
[10] A.V. Dicey, Introduction to the Study of the Law of the Constitution, 5th edition, Macmillan & Co Ltd, 1897, p.194.
[11] Ibid.
[12] Mark D Walters, Dicey on Writing the Law of the Constitution, Oxford Journal of Legal Studies, Vol.32, No.1 (2012), pp.21-49; Lord Bingham, The Rule of Law, Cambridge Law Journal, 66(1), March 2007, p.68.
[13] Steven D Ealy, The Evolution of Rule of Law in Hayek’s Thought 1935-1955, Mercatus Center, George Mason University, Working Paper No 10-38, July 2010.
[14] F.A. Hayek, The Road to Sterfdom, The Institute of Economic Affairs, 2005, p.57.
[15] F.A. Hayek, The Decline of the Rule of Law, The Freemen, April 20, 1953, p.520.
[16] Lord Bingham, The Rule of Law, Cambridge Law Journal, 66(1), March 2007, pp.69-82.
[17] The World Justice Project, Rule of Law Index 2011, p.1.
[18] 管仲《管子·明法》。
[19] 《中國大百科全書》第二版（6），中國大百科全書出版社，2009年，第6-216頁。
[20] 《現代漢語詞典》第六版，商務印書館，2012年，第465頁。
[21] 《辭海》第六版彩圖本（1），上海辭書出版社，2009年，第560頁。
[22] Henry Campbell Black MA, A Dictionary of Law, West Publishing Co, 1891, p.1053.
[23] Bryan A Gardner, Black’s Law Dictionary, 9th edition, West Publishing Co, 2009, p.345，並見Bryan A Garner, A Dictionary of Modern Legal Usage 2nd edition, 法律出版社，2005年，第776頁。
[24] Hilaire Barnett, Constitutional and Administrative Law, 4th edition, Cavendish Publishing Limited, 2002, p.73.
[25] Raoul Colinvaux, Carver’s Carriage by Sea, Vol. 1, 12th edition, Stevens & Sons, 1973, p.7.
[26] John F Wilson, Carriage of Goods by Sea, 7th edition, Pearson, 2010, p.52.
[27] John Rawls, A History of Justice, Harvard University Press, 1971, p.59.