The Prohibition of Inconsistent Behavior
The principle of the prohibition of inconsistent behavior (venire contra factum proprium), which first appeared in Roman law and evolved over the centuries, has now found its place in the “rule of honesty,” which is a fundamental concept of modern legal systems. The rule of honesty, which can be defined as the behavior expected from a person as an honorable and honest person, is the ethical basis that forms the framework of the exercise of rights in our legal system. This rule, which finds its expression in the Swiss and Turkish Civil Codes as a general rule with a wide implementation area, is included in the French, German and Italian Civil Codes only in terms of the interpretation of contracts and the performance of debts. On the other hand, the principle, which is called the prohibition of abuse of right in civil law, has found a wide implementation area in common law --especially American law -- under the name of "estoppel".
The inclusion of the principle of honesty at the beginning of the Turkish Civil Code (“TCC”) shows how fundamental it is. The rule came into existence through Article 2 of the TCC, which states: "Every person must act in good faith in the exercise of his or her rights and in the performance of his or her obligations." The question of abuse of the rule of good faith is dealt with in the second paragraph of the same article as follows: “The manifest abuse of a right is not protected by law.”
Venire contra factum proprium, which is translated into English language as the prohibition of inconsistent behavior, has a place under this umbrella concept, the rule of honesty, and the abuse of right, but it has a separate place from the other appearances and implementations of this umbrella concept. A person who causes the other party to face difficulty by acting in contradiction with their previous behavior, also abuses the other party’s right. For this reason, the prohibition of inconsistent behavior is included under the overall concept of abuse of a right.
As a general principle, there is no rule or legislation that requires consistency in a person's conduct. However, should a person in a legal relationship gain the other party’s fundamental trust, this trust is worthy of protection. Therefore, they can no longer behave in such a way as to undermine the trust they have gained, and they cannot cause distress in the other party with their subsequent behaviors; otherwise, these behaviors may constitute an abuse of right. In other words, in case a feeling of trust worth preserving has been created by prior conduct, and this prior conduct is nullified with a new behavior, inconsistent behavior occurs. Venire contra factum proprium, at this stage, differs from pacta sunt servanda (agreements must be kept). The assumption underlying pacta sunt servanda is that the declared will is binding, whereas in venire contra factum proprium, there is a commitment to the opposite party’s constantina due to trust.
Elements of the Inconsistent Behavior Prohibition
Scholars who have written about this problem generally agree on the elements of the prohibition against inconsistent behavior. The first of these conditions is, undoubtedly, some sort of contradictory or inconsistent behavior. In order to be able to talk about a contradiction in a behavior pattern, first of all, there must be a prior behavior, and then the existence of a second behavior that contradicts this prior behavior. The first behavior gives the other side an impression that they will be treated in a certain way. Everyone in the same situation must have an objective reason for believing that they will be treated in this way. This preliminary action may be performed by an ordinary action or a legal transaction. In fact, even silence may count as a preliminary behavior if it creates a sense of trust. However, the person whose prior behavior is inconsistent is also required to behave wrongfully as well as to break the trust of the other party and to harm them. It is possible to say that the most important line between the freedom of people to change their ideas, attitudes or the freedom of being inconsistent, and violating the rule of honesty is the condition of being at fault which is expressed here. Other conditions noted by scholars include the requirement that the trust created by the preliminary behavior should be worthy of trust, and should not violate principles of legal ethics.
Prohibition of Inconsistent Behavior in Turkish Practice
In many cases in law practice, venire contra factum proprium finds an application area in order to establish the rule of honesty. It is possible to list them as basic categories as follows:
- Creating a sense of confidence in the other party that a right will not be exercised
- Preventing the use of a time-limited right by delaying the other party
- Raising an objection referring to an invalidity or unfairness, which exists in preliminary behavior, when the benefit, arising from invalid or unfair prior behavior, ends
- Losing the use of a right due to the trust created in the other party due to not using it for a long time
- Acting against the trust created in the other party in the way that the contract will be established
- Acting against the trust of the representative by revoking the authorization and by prompting the representative to an unauthorized action
The prohibition against acting inconsistently has also been implemented in Turkish law and the Court of Cassation has prevented the abuse of the rights in the landmark decisions. For example, one of the most typical examples of the abuse of rights with inconsistent behaviors occurs in the real estate construction sector. For many years in Turkey, the contractors had been deliberately concluding real estate sales contracts that did not meet the legal requirements, and following the completion of the project, they had been avoiding the transfer obligation based on the invalidity of the contract. Although this attitude of the contractors was legally correct due to the invalidity of the contract, but it was also against the rule of good faith and the prohibition of inconsistent behavior. The Turkish Court of Cassation, with its decision of joint chambers, dated 30.09.1988, and numbered 1987/2E., 1988/2K.), prevented acting contrary to the created confidence by pointing out the prohibition of inconsistent behavior in the event that the contractor, who initially sells independent sections without a valid contract, delivers them and leaves them to the use of the other party, rejects the transfer of ownership of the independent sections in the title deed (due to the invalidity of the contract).
As mentioned above, in some cases, creating a sense of confidence that a right will not be exercised, by staying silent also creates a prohibition of contradictory behavior. This situation is seen often when the penal clause or compensation claims arising from the contract are demanded after being silent for a long time. In another unpublished decision by the Court of Cassation, dated 30.01.2013, and numbered 2012/19-670E. 2013/171K.,  the court ruled that plaintiff’s claim for compensation after 9 years was an inconsistent behavior and abuse of right since the plaintiff had continued their commercial relations for nine years sending a warning to the defendant in order to terminate the franchise agreement.
In a decision, dated 14.09.2019, and numbered 2008/E. 2009/22810K, the 9th Civil Chamber of the Court of Cassation stated that even if the statute of limitations has expired, if the debtor has acknowledged his debt, his defence based on a statute of limitations will constitute a prohibition of inconsistent behavior and, pursuant to article 2/2 of the TCC, must not be evaluated by the judge.
Although the legal order has given certain rights and powers to individuals to use freely, the use of a right may result in legal but unfair results. Considering that the idea of the legal order is the absolute establishment of fairness and justice, an exceptional power called the "rule of honesty" has been given to the judge to prevent such legal but unfair situations. This power appears in different ways in various fields of law, and the abuse of one's right deliberately by inconsistent behavior is also contained within the rule of honesty. If one party does something that creates a sense of confidence in another party, and then later does or says something that contradicts or undermines that, courts may act to protect the second party, regardless of whether the first party has an otherwise valid claim under the law.
 Oğuzman, M. Kemal ; Barlas, Nami: Medeni Hukuk- Giriş Kaynaklar Temel Kavramlar, Vedat Kitapçılık 2011, p.245
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