The Principle of Legality of Offenses and Penalties: Foreseeability, the Prohibition of Retroactivity and Routes of Recourse

The principle of legality of offenses and penalties ensures that a person is not punished for an act that was not an offense on the date it was committed and is not subjected to a heavier penalty than the one prescribed on that date. It is not enough for the rule to exist only in a statute; its application must be accessible and foreseeable. The creation of a new offense by the administration or the judiciary through interpretation, analogy and retroactive aggravation may give rise to a constitutional problem. [1–3]

This article is for general information purposes. The date of the act, the date the norm entered into force, the nature of the sanction and any amendments in the person’s favor must be examined together on the case file.

What safeguards does legality include?

Article 38 of the Constitution, Articles 2 and 7 of the Turkish Penal Code (TCK) and Article 7 of the European Convention on Human Rights (ECHR) are the main bases. A person must be able to direct their conduct in accordance with the law. For this reason, the elements of the offense and the limits of the sanction must be understandable in advance. Legality is not merely a technical procedural rule for the benefit of the defendant; it is a limit on the power to punish. [1–3]

Under Article 2 of the TCK, offenses and penalties cannot be imposed by the regulatory acts of the administration; analogy cannot be applied in applying the provisions on offenses and penalties. The prohibition of analogy also bars broad interpretations that would lead to analogy. At the same time, it is not expected that every concept in a statute will list all possible cases one by one. The limit of judicial interpretation is assessed on the basis of the essence of the norm and reasonable foreseeability.

Definiteness and the need for interpretation

The use of a general concept in a statute is not in itself a violation. In fields requiring expertise, the fact that a person could foresee the result by obtaining legal assistance may also be taken into account. However, uncertainty cannot reach a breadth that allows the enforcer to punish any act it wishes. The administration’s ease of application does not cure the lack of a statutory basis. [5, §§ 40–44]

In the defense, it is not enough to say only “the provision is uncertain”; it must be shown which element was altered by which interpretation. It should be explained why the act does not fall within the definition in the statute, what the earlier practice was, and why the new interpretation was unforeseeable on the date of the event.

The prohibition of retroactivity and the more favorable law

Article 7 of the TCK provides that no penalty may be imposed for conduct that was not an offense on the date of the act. If a statute that enters into force later has removed the act from the category of offenses or produces a more favorable result, the assessment prescribed by the statute is made. The earlier and later provisions are applied to the specific case and their results are compared. [2]

In determining the more favorable law, a new combined statute cannot be created by selecting only the advantageous parts of different regulations. The elements of the offense, the penalty, the reductions and the related consequences are assessed as a whole by an appropriate method. Temporary or fixed-term statutes and provisions on the enforcement regime have rules of their own; not every new provision is automatically applied to the past.

Procedural change versus substantive criminal rule

That a regulation appears under the heading “procedure” does not by itself determine its real effect. An effect that changes the formation of the offense or the severity of the penalty must be distinguished from a change concerning the conduct of the proceedings. Article 38 of the Constitution also contains a safeguard with regard to the statute of limitations for prosecution and for the penalty and to the consequences of conviction. The transitional provisions of the specific amendment must certainly be read. [1; 2]

Not every change in the enforcement of a sentence has the same legality consequence. A distinction is made between the scope of the adjudged penalty and the manner in which it is enforced. Comparing only the dates on which the regulation entered into force is not enough; it must be shown what legal burden has actually been placed on the person.

Legality in administrative fines

Calling a sanction “administrative” does not mean that criminal safeguards are entirely excluded. The nature, purpose and severity of the sanction are assessed. The statutory framework in the field of misdemeanors (kabahat) and the power of administrative regulation are not unlimited in the same way as the prohibition on creating offenses. The administration’s regulation of a technical detail must be distinguished from its creating a ground for punishment that is not found in the statute. [5]

In the Karlis A.Ş., Application No. 2013/849, April 15, 2014 decision, the subjection of the tachograph exemption recognized in the statute, by means of a circular, to an additional notification condition was examined. The Constitutional Court (Anayasa Mahkemesi) found the imposition of a fine on account of an obligation not found in the statute contrary to the principle of legality. The decision shows that narrowing an exemption by an administrative act may also in effect create a new misdemeanor. [5, §§ 40–44]

This conclusion does not mean that all technical regulation provisions are invalid. The real question is whether details are being regulated within the field drawn by the statute, or whether criminal liability not provided for by the statute is being created.

Reliance on assumption instead of personal conduct

In the Mehmet Güzeloğlu, Application No. 2014/3134, May 7, 2015 decision, the Constitutional Court examined the expansion of the scope of a statutory regulation on the basis of an assumption. The failure to clearly assess, within the limits of the statute, the link between the act and the applicant led to a violation of legality. [6, §§ 32–38]

The decision shows that a legality defense sometimes needs to be addressed together with personal responsibility and the attribution of the act. Even so, insufficiency of evidence and unforeseeable expansion of the norm are not the same claim. Instead of saying “I did not commit the offense” to the Constitutional Court, it should be explained which statutory element the court changed and how.

Timeline and norm table for an effective defense

Only today’s text in force should not be placed in the table. For an old act, the official text of the old norm should also be included in the file. The dates of adoption, publication and entry into force of an amendment may differ. In annulment decisions of the Constitutional Court, the postponement of entry into force and the effect of the annulment are examined separately; an annulment decision does not automatically eliminate every past judgment.

The counter-argument may be that the practice has long been the same or that the person could foresee the result because of their professional position. In that case, the similarity of earlier decisions to the event, the accessibility of the interpretation and its connection with the wording of the statute should be discussed. The existence of a single earlier decision does not automatically prove that the whole practice was foreseeable.

Ordinary routes of recourse and the Constitutional Court

A legality objection must be raised expressly during the investigation and the trial. The act described in the indictment should be compared with the norm, the request for the more favorable law should be made concrete, and the answer given in the reasoned judgment should be checked. The same basic problem should be pursued in the applicable appeals to the regional court of appeal (istinaf) and the Court of Cassation (Yargıtay). For administrative sanctions, the competent authority is determined under the special statute. [7]

In criminal proceedings, with regard to the current time limits for appeals to the regional court of appeal and the Court of Cassation, the notification of the reasoned judgment and the transitional provisions are important. It cannot be assumed that the same time limits apply to an administrative fine. The notice of legal remedy should be read, but the possibility that the notice is erroneous should also be checked against the norm.

As a rule, an application to the Constitutional Court is made within thirty days after the relevant effective remedies have been exhausted. The applicant must clearly establish the link between the act, the norm, time and interpretation. An individual application is not an abstract annulment action against a statute; a personal and current interference must be shown. Nor is the Constitutional Court an appeal authority that redoes every legal interpretation of the ordinary court. [8]

Attorneys may use the UYAP Attorney Portal. The norm on the date of the event, the text of the amendment, the reasoned judgment, the petitions filed in the legal remedies and the record of learning should be attached. The claim in the application form should not be left as a matter expected to be understood only from the annexes. [9]

Consequences of a violation decision

If the violation arises from a court decision, a retrial is an important form of redress. The relevant court must make an assessment that removes the cause of the violation identified by the Constitutional Court. An individual application decision does not have the same effect as the annulment of a norm for all persons. If compensation is sought, the connection between the loss and the violation is explained separately. [8, Art. 50]

As regards the European Court of Human Rights (ECtHR), the safeguard of Article 7 of the ECHR may be assessed within the framework of domestic remedies and the general four-month time limit. Failure to apply properly to the Constitutional Court may also give rise to an admissibility problem at the later stage. [3]

Our articles on appeal in a criminal case and retrial after a Constitutional Court violation decision complete the process.

The legality safeguard is not merely the existence of a text

The comparative study by Alaaddin Egemenoğlu and Mustafa Eren Güçarslan addresses the accessibility, definiteness and foreseeability aspects of the principle of legality together. Reflecting this approach in a case file means not being content with asking merely whether a statutory provision exists. Whether, on the date of the act, the person could reasonably foresee the criminal consequence of their conduct and whether the court’s interpretation exceeds the limits of the norm should be made concrete. [10]

How should a legality claim be built on the specific provision?

What was prohibited on the date of the act must be shown

In the defense, the date on which the act took place and the regulation in force on that date are determined first. Then it is shown which conduct was considered to fall within which provision in the indictment or the sanction decision. Instead of a general statement such as “there is no offense in the statute”, the elements of the regulation and the specific conduct attributed to the person should be examined side by side. If it is claimed that an element was completed by the court through assumption or expanded by an administrative regulation, the change must be shown clearly. [1; 2]

The existence of the statutory text is not sufficient on its own; it is also important that the person could reasonably foresee the criminal consequence of their conduct on the date of the act. However, not every difference in interpretation amounts to unforeseeability. The relationship of the judicial interpretation to the essence of the provision, the earlier practice and the nature of the event are assessed together. Instead of treating every interpretation unfavorable to it as analogy, the defense should explain why the interpretation exceeded the statutory limit. [3; 10]

No selective combination should be made in comparing the more favorable law

Whether regulations amended after the date of the offense are more favorable is not determined by looking only at the lower limit of the prison sentence. The legal situation that would arise from the application of the relevant regulation must be assessed as a whole. It is not correct to combine one part of the old provision with another part of the new provision and form a new sanction regime that is not found in the statute. The transitional provisions and whether the amendment is a substantive criminal rule or a procedural rule are also examined separately. [2, Art. 7]

An attorney may show the dates of the amendments and the result each regulation would produce in the specific file by means of a short comparison table. If it is claimed that the comparison made by the court is incomplete, it should be stated which result was overlooked. Raising the objection expressly at the appeal stage, whether before the regional court of appeal or the Court of Cassation, is also important for the subsidiarity assessment before the Constitutional Court. [7; 8]

Misdemeanor and disciplinary sanctions are not the same category

That a sanction is called administrative in domestic law does not mean that constitutional safeguards will not apply in any form. On the other hand, it cannot be said that all disciplinary measures are subject to exactly the same regime as the offenses in the TCK. The nature and severity of the sanction, the statutory regulation and the special protection of the relevant right must be determined. In an expulsion from education, the safeguard of a statutory basis under the right to education, and in an administrative fine, the review of the legality of offenses and penalties, should not be merged in the same sentence. [1; 3; 5]

The concrete contribution of the Karlis A.Ş. decision is that administrative practice changing the limits of a statutory exemption may be the subject of constitutional review. The decision should not be reported as saying that every circular or implementing instruction is automatically invalid. The issue is by what act the field recognized by the statute was narrowed to the person’s detriment. [5]

The request to the Constitutional Court is not framed as asking for a new statute to be written or for all similar penalties to be abolished collectively. The applicant’s own sanction, the effective remedies used and the decision that could redress the consequences of the violation are explained. A strong norm review on the merits of the alleged violation does not by itself cure deficiencies in time limits and in the avenue of application.

Foreseeability does not mean that every dispute has been resolved in advance

That a criminal norm is foreseeable does not require that all the cases to which it may be applied be listed one by one in the statute. General concepts may be used and courts may interpret these concepts. The constitutional question is whether the limit that allows the person to reasonably foresee the criminal consequence of their conduct has been exceeded. The applicant should not be content with saying only that there was no decision on the same event before the applicant’s case; it should be explained why the interpretation given is incompatible with the text and application of the norm. [1–3]

Particularly in professional or technical activities, the person’s opportunity to learn the relevant regulation may also be included in the assessment. However, having expertise does not create an obligation to know in advance every expansive interpretation that the administration or the court later formulates. The relationship between the existing statute, the relevant secondary regulation and practice should be shown. If the alleged uncertainty affects in respect of which element the specific conduct will be punished, the constitutional claim becomes clearer.

Can an administrative regulation expand the sanction field in the statute?

The determination of technical details by administrative regulations must be distinguished from the addition of a new element to the scope of an offense or sanction. The limit of the power granted by the statute, the function of the administrative text and the sanction applied to the person are examined together. It is not sufficient to state in the application only that there is a regulation or a circular. The field regulated by the statute and the additional condition introduced by the administrative text should be compared. In particular, if the narrowing of an exemption, a new obligation or the emergence of a new sanction is under discussion, it must be shown how this change came about. [1, 2, 5]

In the Karlis AŞ decision, the relationship between the regulation on the tachograph exemption and the condition introduced by circular is important in this respect. The value of the decision lies in its focus on the statutory basis of the sanction rather than on the name of the administrative act. It cannot be concluded that every circular is unlawful or that the administration can give no technical explanation. The main question is whether the specific sanction remains within the framework provided for by the statute. When using a precedent, it should be explained whether in the applicant’s case there is the same kind of expansion of scope. [5]

How is the comparison of the more favorable law made understandable?

In a claim for a more favorable regulation, showing only the amount of the penalty in the new statute is sometimes not enough. The elements of the offense, the type of sanction, the lower and upper limits, special reductions and other relevant provisions should be assessed together. The result that emerges from applying the old and the new regulations separately to the specific case is compared. Creating a hybrid application that is not found in the statute by selecting the advantageous provisions of different periods is not the same as a review of the more favorable law. [2, Art. 7]

The petition should state clearly which amendment produces which result. For example, a reduction in the sanction, the conduct ceasing to be an offense and a change made only in procedure are different legal problems. An abstract statement such as “the new statute is more favorable” may not point to the specific point that the court has to assess. For this reason, the dates on which the norms entered into force, the date of the event and the date of the judgment should be followed together. Instead of relaying only the title of an amendment or a press release, the Official Gazette (Resmî Gazete) and the entry-into-force provisions should be checked.

The error of confusing a substantive criminal rule with a procedural rule

Not every procedural change results in the removal or reduction of the penalty with regard to earlier events. A change in the time limit for application, in the competent authority or in the method of trial and a change in the scope of the offense are examined separately. What matters is not only in which part of the statute the rule is found but also what it actually regulates. If there is a transitional provision in the specific file, it must be applied separately. A general sentence such as “non-retroactivity” cannot resolve all the problems of application over time. [1, 2, 7]

How is the constitutional problem shown in the ordinary legal remedy?

In an appeal to the regional court of appeal or the Court of Cassation, the legality claim should be built by indicating which part of the judgment is being challenged. Under which concept did the court place the conduct? In what way was this scope explained earlier? Which link between the defendant’s act and the elements of the norm has not been established? The answers to the questions distinguish an objection to the evaluation of evidence alone from a legality problem. The Constitutional Court is not a general appeal authority that re-examines every interpretive error of a criminal court. [6–8]

In using the Mehmet Güzeloğlu decision as well, relaying the finding of violation is not enough; the constitutional reasoning on the limit of application of the norm should be taken as the basis. The applicant should clearly show what the expansion or unforeseeability in their own case is. The court’s characterizing the same conduct differently does not by itself lead to a violation of legality. How the alleged problem affects the statutory framework of the offense or the penalty should be explained. [6]

Finally, the request should be appropriate to the problem identified. A constitutional violation decision does not directly replace a judgment of acquittal in every file. If a retrial is necessary, the relevant court must decide by removing the cause of the violation. Establishing a link in the application form between the request for relief and the explanation of the violation prevents the discussion of the norm from remaining an abstract legal opinion. The current and personal effect should be shown through the consequences the decision has had for the applicant. [8]

For the details of the subject, you may also see our articles on the right not to be tried twice for the same act, the presumption of innocence and the right not to be stigmatized and the limit between terrorist propaganda and freedom of expression. For our firm’s work in this field, you may see the page on Constitutional Court and ECtHR applications.

Conclusion

Four questions are at the center of a legality defense: when was the act committed, what norm existed on that date, how was the norm interpreted and what sanction was applied to the person? Once this link is established, an ordinary evidentiary objection can be separated from a constitutional legality problem. Preserving the text in force on the date of the event, as much as the current norm, is the basis of pursuing one’s rights.

Frequently Asked Questions

Can an offense be created by regulation?

Under Article 2 of the TCK, offenses and penalties cannot be imposed by the regulatory acts of the administration. The regulation of technical details is assessed separately.

Is a new statute always applied to the past?

No. The prohibition of retroactivity to the detriment of the person, the more favorable law and special transitional provisions must be distinguished.

Is every broad interpretation a violation of legality?

No. The relationship of the interpretation to the essence of the norm and its foreseeability are examined; an expansion amounting to analogy is prohibited.

Are administrative fines outside the safeguard?

Not automatically. The nature of the sanction and its statutory basis are assessed.

Does the Constitutional Court re-evaluate all the evidence?

No. A legality complaint should focus on the claim that the court applied the norm outside constitutional limits.

Does a Constitutional Court violation finding annul the statute for everyone?

An individual application decision is not the same as norm review; it is aimed at redressing the violation in the application.

Sources and legal bases

[1] Constitution, Art. 38. Text.

[2] Turkish Penal Code No. 5237, Arts. 2, 7. Text.

[3] ECHR, Arts. 7, 35. Text.

[5] Constitutional Court, Karlis A.Ş., Application No. 2013/849, April 15, 2014. Decision.

[6] Constitutional Court, Mehmet Güzeloğlu, Application No. 2014/3134, May 7, 2015. Decision.

[7] Code of Criminal Procedure No. 5271, Arts. 273, 291. Text.

[8] Law No. 6216, Arts. 45–50. Text.

[9] Constitutional Court, UYAP Attorney Portal application guide. Guide.

[10] Alaaddin Egemenoğlu and Mustafa Eren Güçarslan, “Evaluation of the Principle of Legality in Offenses and Penalties in Turkish and German Criminal Law within the Framework of Foreseeability and the Safeguard Function” (“Öngörülebilirlik ve Güvence Fonksiyonu Çerçevesinde Suçta ve Cezada Kanunilik İlkesinin Türk ve Alman Ceza Hukuku Açısından Değerlendirilmesi”), Journal of the Faculty of Law of İnönü University, 17/1, 2026, pp. 1–19. Study.