The problem of error in substantia

(a) Ulp. D. 18, 1, 9, 2

The most intriguing and disputed kind of mistake considered by the Roman lawyers is error in substantia. The core fragment stems, again, from Ulpian's commentary on Sabinus.

"Inde quaeritur, si in ipso corpore non erratur, sed in substantia error sit, ut puta si acetum pro vino vencat, aes pro auro vel plumbum pro argento vcl quid aliud argento simile, an emptio et venditio sit. Marcelius scripsit... emptionem esse et venditionem, quia in corpus consensum est, etsi in materia sit erratum, ego in vino quidem consentio, quia eadem prope... owia est, si modo vinum acuit: ceterum si vinum non acuit, sed ab initio acetum fuit, ut embamma, aliud pro alio venisse videtur, in ceteris autem nullam esse venditionem puto, quotiens in materia erratur."^{[3068] [3069]}

A variety of examples are presented: vinegar is sold as wine, bronze as gold, lead or some other metal resembling silver as silver. Clearly, we are not dealing with an error in corpore. The parties do not disagree as to the object of their contract of sale, for they both have the same specimen of liquid, the same lump of metal in mind. But the purchaser is seriously disadvantaged by the deal, for the liquid has turned out to be vinegar instead of wine, the metal is not gold, as he had thought, but it is bronze, etc. He has erred as to what the object of the sale really consisted of; his mistake relates to the substance of the thing. This is the crucial feature of the problem. Whether the vendor was labouring under the same mistake, we do not know. Ulpian seems to regard that as immaterial.^[3070] "Aliud pro alio venire" appears to indicate that the purchaser's error is not spontaneous, but has been induced by the seller.^[3071] But whether there was, to use the terminology of English law, fraudulent or innocent misrepresentation cannot be gauged from the text.

(b) Error relating to quality

The situation was quite different, however, if the purchaser's mistake did not relate to the substantia (sometimes also the terms "materia" or "qualitas" are used),^[3072] but merely to the quality of the object of sale: "Aliter atque si aurum quidem fuerit, deterius autem quam emptor existimaret: tune enim emptio valet."^[3073] Here the object sold is gold, but the gold is of a lesser quality than the purchaser was entitled to expect. We are dealing with a latent defect, a type of situation for which, as we have seen,^[3074] a different set of rules applied. After all, by the time of classical Roman law, the days of an austere and categorical "caveat emptor" policy were gone and the purchaser was well protected. The sale of slaves and cattle was governed by the aedilitian remedies, whereas the purchaser of other goods was able to avail himself of the actio empti: for damages in case of dolus and breach of formless dicta in venditione or formal promissa, for quanti minor is or redhibition even against the honest vendor. The applicability of these remedies, of course, depended on the validity of the sale: without emptio venditio, no actio empti and no aedilitian remedies were available. It furthermore depended on the existence of a (latent) defect. Bronze, however, can hardly be said to be defective gold, nor can lead be regarded as defective silver.

(c) Drawing the line: vinegar sold as wine

As a result of this, it became necessary to draw a line between cases where the object of the contract suffered from a defect and where it turned out to be of an entirely different substance. Obviously, this could involve some very fine distinctions. Apart from that, differences of opinion were bound to arise as to the proper solution of individual cases; after all, there was not even unanimity about whether error in substantia should be taken into consideration at all! Hence, it is very difficult to find a common denominator for the casuistry contained in the Digest title 18, I.^[3076] Ulpian refers to the oricna, the "being", the nature or the essence of the object, and he illustrates this vaguely philosophical criterion^ with the wine/vinegar example. Where something has been sold as wine that was in fact once wine but turned into vinegar in the meantime, the sale is valid. The wine has undergone acetic fermentation, an organic process which makes it unpalatable and destroys most of its commercial value; but the liquid is still virtually of one and the same continuous being.^4fl The vinegar, in this instance, is wine turned sour (i.e. bad). The situation was different, where the vinegar sold as wine was (wine) vinegar from the start, and had been specifically prepared as such. Here, the object of the sale was neither wine nor wine turned sour, but an alternative substance. Despite the common origin of wine and vinegar in grape juice, the liquid in question never had the (original) "wineness" envisaged by the purchaser.

(d) Further borderline cases

Problems could arise in cases where the object of the sale contained at least some of the material of which it was supposed to consist in its, entirety. We have seen that the contract is valid if the gold is merely of a lower quality than the purchaser expected. It is void if it is not gold but bronze. In D. 18, 1, 14 Ulpian discusses the sale of a bracelet said to be of gold but containing only "auri aliquid": the contract is valid. The same holds true, if it was gilded: "narn si inauratum aliquid sit, licet ego aureum putem, valet venditio." This statement is in direct conflict with an earlier opinion of Julian, concerning a silver-plated table which the parties believed to be of solid silver: "Mensam argento coopertam mihi ignoranti pro solida vendidisti imprudens: nulla est emptio pecuniaque eo nomine data condicetur."^{[3077] [3078] [3079] Various attempts have been made to reconcile these texts.[3080] [3081] It is more likely, however, that there was a difference of opinion between the two jurists. By insisting that the object must have consisted, in its entirety, of a different material, Ulpian limited the scope of the error in substantia doctrine not inconsiderably.}

Not in all cases, however, could the line be drawn so easily... si ego mulierem venderem, tu puerum emere existimasti, quia in sexu error est, nulla emptio, nulla venditio est."⁴⁹ A female slave was bought in the belief that she was a man. Here the purchaser's mistake obviously did not relate to the material of the object of sale: both male and female slaves are made of flesh and blood. Nevertheless, mistake as to the sex of a slave was regarded as "substantial". Men and women are essentially different; few persons of the female sex would presumably like to see themselves described as defective males.

The definition drawn in D. 18, 1, 11, 1 thus demonstrates that the problem of error in substantia was not simply reduced to a question of material. At least, therefore, in the writings of Ulpian, and in spite of D. 18, 1, 14, we still find a fairly wide concept of substantia. This casts some doubt over the thesis recently advanced by Frier^[3083] that later classical jurists took a strongly negative stance towards error in substantia, and that its field of application was insignificant in practice.