Essential elements
There are basically three requirements that, in almost all legal systems, the laws require to achieve the effectiveness of the contract: consent, object and cause.
It is the volitional element, the internal will, the will that, manifested under consent, produces legal effects. The perfection of the contract requires that consent be freely given by all the parties involved, due to or effect of the principle of relativity of contracts. The will is expressed by the successive concurrence of the offer and acceptance"), in relation to the thing and the cause that must constitute the contract. Vitiated consent will be void, for having been given by mistake, with violence or intimidation, or fraud, or by a subject other than the object of the contract.
The absence of defects in the consent is essential for the validity and effectiveness of the contract, to which end it is required that the will not be pressured by external factors that modify the true intention. The most prominent vices of consent are: (a) error, (b) violence and (c) fraud.
The error must not be in bad faith, because otherwise, it becomes fraud.
All things "Thing (Right)") that are not outside the commerce of men, even future things, can be the object of contracts. All services "Service (economy)") that are not contrary to laws, morality, good customs or public order may also be the subject of a contract.
Normally, the civil regulations of legal systems require that there be a just cause for the birth of legal acts. The cause is the determining reason that led the parties to enter into the contract.
A contract has no cause when the manifestations of will do not correspond to the social function that it must fulfill, nor when a cause is simulated or feigned. The contract must have a cause and this must be existing, true and lawful.
The problem of cause revolves around the 'final cause'. There have been disagreements and debates that still remain active about whether the final cause should be considered an essential element of legal acts. Apparently due to the wording of Art. 944 of the CC it should be. For those who consider that the final cause should not be part of the essential elements of the legal act, they express that it is confused with its object or with its consent. This position affirms that the essential elements of business are: subject, object and form. But for those who consider that the final cause is part of the legal business, they distinguish:
Jean Domat was the first to develop the causalist theory of obligations; he maintained that the cause of obligations resided in the consideration exercised by one person in relation to another. His doctrine was followed and disseminated by his disciple Robert-Joseph Pothier, and was later included in the French Civil Code of 1804. These causalists distinguished synallagmatic contracts from real, unilateral contracts and those with free titles. Domat and Pothier required as an element for the validity of a contract "a lawful cause in the obligation."
When the French doctrine of causalism was at its peak"), in 1826 an essay by the Belgian A.-N.-J. Ernst appears, entitled "The cause is an essential element of the contractual obligation." different elements and require four conditions: will, capacity, object and cause, when in reality there are only three. If in gratuitous contracts the cause resides in the freedom of the benefactor, it is also not true that this is in itself an external condition of the existence of such contracts. A feeling that animates the donor cannot be separated from the will that she expresses, to make it an element of the contract.
Planiol affirms that: "The cause is false and useless." It is false because if it is said that in bilateral contracts the cause of the obligation of one of the parties is the performance of the other, it forgets that the performance and the obligation arise at the same time and it is not possible for one thing to be the cause of the other. Most French and European causalists have turned to these theories.
At the end of the century and the beginning of the century, neocausalists have appeared. Indeed, Henri Capitant"), Jacques Maury") and Louis Josserand have revived the theories of Domat and Pothier. The neocausalists were objectivists, they maintained that the cause element is essentially a psychological factor, they conceive the cause as the concrete end, the purpose, the interest that induces the parties to contract, the immediate and determining end that they have had in mind. There is no will without an interest. Modern codes have eliminated the cause in their legislation, others have incorporated it, but there is a marked interest in eliminating it from current codes.
In general terms we can affirm that the Argentine Civil Code alludes to the cause, in its art. 417, when it provides that: The obligations derive from any of the sources established by law. As can be seen, this article incorporates a causalist notion of obligations. Now, when we talk about the cause in the new code, it can be said that practically nothing has changed in relation to its predecessor, we are referring to the Vélez Sarfield code.
Accidental elements
They are those that the parties establish through special clauses, which are not contrary to the law, morality, good customs, or public order. For example: the term, the condition "Condition (Law)"), the mode "Mode (law)"), solidarity, indivisibility, representation, etc.
In accordance with the autonomy of the will, the contracting parties can establish the agreements, clauses and conditions that they deem appropriate, as long as they are not contrary to the law, morality, good practices and customs, or public order.