Chapter I. On the Definition and Divisions of Contracts

A contract is an agreement by which one or more persons oblige themselves toward one or more persons to give, do, or omit something. Moreover, it is distinguished in many ways; for it is:

1st. Unilateral, which is also called gratuitous, or bilateral, which is also called onerous. The former occurs when one or more persons oblige themselves toward one or more persons not obliged, as in the contract of a gratuitous promise. The latter is had when one or more persons oblige themselves toward one or more persons likewise obliged, as in exchanges. Besides, this latter is again subdivided into commutative and aleatory. It is commutative if one contracting party gives a thing in one species and the other gives an equivalent thing of the same or of a different species. It is aleatory if one gives a thing, but the other contracting party gives not a thing but the probable hope of obtaining some thing; and since this hope can fail, it causes a contract of this sort to bear the likeness of chance.

2nd. Solemn or simple, according as it requires special formalities of law, or is subject only to common dispositions.

3rd. Named and unnamed, according as it has a proper name, as, for example, sale, or lacks a proper name, for example, I give that you may give, I do that you may do, etc.

4th. Naked or vested: a contract is called naked when it lacks every support of law and therefore obliges only in conscience; but it is called vested if it has some support of law by which it gives rise to a civil action. Supports of law are writing, stipulation, witnesses, oath, etc.

5th. Formal or express, or virtual or tacit. The former is that which is made by words, writings, or other signs explicitly manifesting consent; but the latter is that whose consent to the agreed thing indeed exists really, but is manifested only implicitly by some saying or deed. Thus a physician exercising his art is judged to promise that he will do that which his profession requires. This contract is also commonly called a quasi-contract.

6th. Absolute or conditioned, according as no condition or some condition is placed upon it. It is also called pure or not pure.

Whatever civil law in the territory establishes concerning contracts, both in general and in species, whether named or unnamed, and concerning payments, the same things are to be observed by canon law in ecclesiastical matter with the same effects, unless they are contrary to divine law or something else is provided by canon law (Can. 1529).