In Roman law, the relation between "jus" and "aequitas" is expressed by the term "interpretation "We are accustomed to understand by the term 'interpretation' that function of the mind which attempts to find the meaning of a legal rule, especially a written rule; an endeavor to discover the intention of its author. The manner of 'interpretatio,' however, which is ascribed to the Roman jurisprudents was not of a character so exclusively passive, as we might say. Rather it included the task of adding to the written law what remained still unwritten, to supplement the former by the latter. They were intermediators, so to speak, between the letter of the statute and real life, and as such it was their business not to stick to the literal contents of the statute and the original intention of the legislator, but to adapt the letter to the needs of actual life and to make the application of the statute practicable."9
The interesting thing in this is, for us, the light it throws upon legal method. In the science of legal sources it is formally recognized that legal science may actually formulate new law, and this fact is expressed by a specific concept. For the result of such "interpretatio" is precisely what is called "jus non scriptum" in the specifically Roman sense. This form of unwritten law consists of the supplementary matter, the intellectual surplus so to speak, which was added to the written law (meaning the text of statutes) by the interpretative activity of the "prudentes."
Accordingly, the concept "unwritten law" is identified by Pomponius with that of "lawyers' law": is properly emphasized by Sternberg (in Zentralb. R. W. vol. 26, p. 65); in this place, to be sure, we can, for lack of space, give nothing but the most sketchy synopsis.
9 Puchta, "Kursus der Institutionen," vol. 1 (4. edition, 1853), p. 316.
"Haec disputatio et hoc jus, quod sine scripto venit compositum a prudentibus, propria parte aliqua non appellatur, . . . sed communi nomine appellatur jus civile."10
Still more distinctly it is declared in the next paragraph that this "jus civile," which properly means the "jus non scriptum" in question, had its origin in the creative power of "interpretatio":
"Lege XII tabulorum ex his fluere coepit jus civile. Omnium tamen harum . . . interpretandi scientia apud collegium pontificum erat . . . et fere populus annis prope centum hac consuetudine usus est."11
And finally: " . . . proprium jus civile quod sine scripto in sola prudentium interpretatione con-sistit."12
Ehrlich's enduring merit is to have emphasized strongly that in these places the concept of the "jus civile" proper has been defined "in a manner that cannot be misunderstood."13 From this, then, we learn that the specifically Roman idea of the unwritten law was that it consisted "simply of the interpretations of the jurisprudents." According to the Roman view, it is nothing more than the result of interpretation of the written law.
10 Dig. 7, 2, 2,5.
11 Dig. 7, 2, 2, 6.
12 Dig. 7,2,2, 12.
13 Ehrlich "Beitrage zur Theorie der Rechtsquellen," I. Teil. Das "jus civile, jus publicum," etc. Berlin 1902, pp. 1 seq. But cf. also: Jhering, "Geist des romischen Rechts," passim; Kruger, "Geschichte der Quellen und Literatur des romischen Rechts" (1886), pp. 26 seq.; Karlowa, "Romische Rechtsgeschichte" (1885), pp. 454 seq.; Joers, "Romische Rechtswissenschaft zur Zeit der Republik bis auf die Cato-nen" (1888), pp. 71 seq.; Sohm, "Institutionen" (13. edition, 1908), pp. 8 seq. (The last two named begin to show the influence of Ehrlich.) See also Pernice, "Zum romischen Gewohnheitsrecht," Zeitschrift der Savigny-Stiftung fur Rechtsgeschichte, Romische Abteilung 20, p. 151; and Lambert, "La Fonction du droit civil compare," 1903, pp. 694 seq.
As a matter of fact, this notion is of Greek origin.14 It occurs especially in Aristotle, whose means also the lawyers' law formulated by "equitable" decisions.15 It is very important, in this connection, to understand the conception ofthe Greek equivalent of "aequitas," which is nothing less than "the foundation of the whole system of law." In the meaning of Aristotle, it is "the law correctly understood and interpreted," such as is always aimed at by positive law. It also forms a principle of interpretation, for the positive law must be interpreted and conceived in accordance with The written law is the literal text of the statute,16 the unwritten law means the perfect meaning of it which cannot be expressly set forth for each individual case.
To explain this meaning, Aristotle says "that the 'equitable' is indeed 'just' but not equivalent to the 'legal.' It is rather an improvement on the merely legally-just. The reason is that every statute speaks in general terms, yet many things cannot be expressed generally. Therefore, in matters where one is compelled to speak generally but is not able to do so correctly, the statute regards only the majority of cases, although well knowing that this is an error. Nor is this manner of speaking improper on that account, for the fault is not in the statute or the legislator, but in the nature of the thing itself." Then he adds: "Now, where the statute reads generally but a case comes up that will not fit into these general expressions, one proceeds quite properly if, wherever the legislator has failed to provide therefor and by his general expression has committed a mistake, one corrects the omission in such a manner as the legislator himself would speak and legislate if he were present to witness the case."
14 Cf. Ulpianus, Digest 1, 1, 6, 1.: "Hoc igitur jus nostrum constat aut ex scripto aut sine scripto . . . ut apud Graecos: T . . . "; similarly, Inst. 1, 2, 3.
15 Hirzel, (Abhandl. der philologisch-historischen Classe der Konigl. Sachsischen Gesellschaft der Wissenschaften 20, 1. Leipzig 1900); same, "Themis, Dike und Verwandtes," Leipzig 1907, pp. 359 seq.; Cathrein, S. J., "Recht, Naturrecht," etc. (1901), pp. 101-102; also Voigt, "Das jus naturale," vol. 1, pp. 127, 175, 529, and vol. 4, p. 372; Pernice, "Parerga," Z. Sav. f. Rg. 22 (1901). pp. 82-95; Kraus, Griinhut's Zeitschrift, 32, p. 613.
16 Cf. Aristotle, "Rhetoric," A. 10. 1368 b7. A. 13. 1373 b4; and especially "Nicomach. Ethics," E 14, 1137.
Thus equity is "an improvement of the statute where it commits a mistake by reason of its general expression." "This also is the reason why all things cannot be regulated by statute; for about some things it is not possible to enact a law."17
What the Greeks thus call is equivalent to the Roman "aequitas," the foundation of the celebrated 'interpretatio jurisprudentium," which according to Pomponius is identical with "jus non scriptum."