While the previous parts of Wolff’s Jus naturae have been at least partially thematic unities, the fifth part is the first exception and feels like just an appendix to the previous part that dealt with various types of contract. Indeed, the first chapter of this book merely continues the discussion of reciprocal contracts, in which all sides provide something to others.
A first new kind of contract dealt by Wolff is cambium, that is, any contract, in which money is exchanged for money. The most straightforward case of cambium is a contract where a person exchanges currency of one country to currency of another country. Wolff notes that there are people who provide large quantities of money just for these types of transactions and that these money changers have the right to ask a payment to cover the costs of their profession.
A more intricate sort of cambium is what Wolff calls cambium trassata, in which a person (campsarius or remittens) gives money to another person (campsor or trassans), who promises to take care that a third person (acceptans or trassatus) will give the same amount of money to a fourth person (praesentans). This rather complex sounding contract was quite a common way to provide travelers with enough money, without the need of carrying actual metal coins from one place to another, but instead using written notes or litteras cambiales (bills of exchange) detailing such contracts. They are first examples of a modern system of banking, and importantly, Wolff notes that such money contracts are inherently rational and in accordance with the natural law.
Wolff goes into great details into finesses such as who is obligated to pay, if the acceptans does not want to give the agreed sum of money to praesentans, and what should praesentans do to get her money in such a case. The most important additional point Wolff makes is that praesentans can transfer her right to get the money to another person, thus making it possible to use bills of exchange as a rudimentary form of paper money.
A third form of cambium Wolff mentions is cambium siccum, in which a person receives money from another and in return gives the other chirographum, in other words, a document in which she promises to pay the other person the same amount of money at a later date - in effect, this is just another form of loan.A further point with chirographum is that, like bills of exchange, they can be sold further.
At this point, Wolff also mentions two other documents related to loans and in general to any debt. The first one - apocha or quittancia - is a document written by the creditor, in which she declares that the debtor has paid her debt. The other one, antapocha, is, on the contrary, a declaration written by the debtor that she has paid the debt. Wolff notes that all the three documents have merely evidential weight and they do not as such create or cancel debts - thus, even if a person has lost e.g. a chirographum given to her, she is still entitled to the promised sum.
In addition to cambium contracts, Wolff considers what he calls contractus aestimatorius, in which a person gives something for another person to be sold for a certain price. If this other person manages to sell the thing for a larger sum of money, she can keep the difference; if she manages to get less than agreed, she will have to pay the rest. She can also keep the thing, if she just pays the whole price agreed, or she can return it to the first person. It is not decided whether, together with the possession of the thing, also its ownership is transferred to the second person, and the contract can be made in both ways. In some cases the choice of the owner is even significant. For instance, if the thing in question produces more wealth at the time when it is with the second person for sale (say, if the thing in question is a herd of cows that gets bigger), this additional wealth belongs to the owner.
Some types of contract Wolff deals in the first chapter of the book seem like minor and even insignificant modifications of earlier types of contract. Such is, for instance, constitutum, in which a person promises to fulfill an earlier obligation, whether it is her own or someone else’s - in the former case, constitutum means simply a reaffirmation of an old obligation, while in the second case, it is quite similar to fidejussio or a guarantee for another person’s obligation. Another case is contractum institorium, which is essentially a combination of two earlier types of contracts: locatio conductio and mandatum. In effect, in contractum institorium a person hires another person to do business deals in her name.
Wolff also suggests a reclassification of all the bilateral contracts into do ut des -, facio ut facias and do ut facias -contracts - that is, contracts where both sides give something to the other side, contracts where both sides do some work for the other and contracts where one side gives and the other side does something. Wolff ties this classification with his notion of the development of economy. In the primeval times, Wolff notes, when no one owned anything, people could only exchange work with one another. The introduction of ownership, he has already noted in earlier books, is a good thing, and now he finds yet another reason for its introduction - ownership of things allows new kinds of contracts, in which ownership of things changes.
