The school of legal positivism was born as a response to the dominance of natural law thought that places morality, religion, and universal values as the basis for the applicability of law5. In the 19th century to the beginning of the 20th century, the development of the modern state demanded a legal system that was able to provide certainty, order, and uniformity in people's lives. This condition encouraged jurists to separate the law from non-juridical elements so that the law could be understood as a system of norms that stood alone. The applicability of a law in the view of legal positivism is not determined by the fairness or not of the content of the law, but by the procedure for its formation in accordance with the applicable rules. Therefore, this school emphasizes the importance of legal certainty as the main goal in the implementation of the legal system.

The development of the school of legal positivism cannot be separated from the contributions of thinkers such as Jeremy Bentham, John Austin, and Hans Kelsen. If Bentham and Austin are known as the pioneers of classical legal positivism, then Hans Kelsen is considered a figure who perfected legal positivism through a more systematic and scientific approach. Kelsen's thought seeks to answer the question of why. A legal norm can be considered valid as well as how the relationship between legal norms in a legal system is. This contribution makes Kelsen one of the most influential figures in the development of modern legal philosophy.

Hans Kelsen was born on October 11, 1881 in Prague, which at the time was part of the Austro-Hungarian Empire, to a Jewish family that later settled in Vienna, Austria6. His father was named Adolf Kelsen and his mother was named Auguste Löwy. From a young age, Kelsen showed a great interest in science, especially in the fields of law and philosophy. He studied law at the University of Vienna and later developed into an academic and legal expert who had a great influence on the development of modern legal theory. In addition to being known as a legal philosopher, Kelsen also played a role in drafting the Austrian Constitution of 1920 and was a judge at the Austrian Constitutional Court.

Hans Kelsen's thought was heavily influenced by Neo-Kantian philosophy which distinguishes between the world of facts (sein) and the world of norms (sollen)7. This influence encouraged Kelsen to view law as a system of norms that must be studied separately from political, moral, religious, and sociological aspects. According to Kelsen, law cannot be explained only through social facts, but must be understood based on norms that govern human behavior. This view then became the basis for the birth of a legal theory known as the Pure Theory of Law or Pure Law Theory.

Hans Kelsen's most famous monumental work is Pure Theory of Law (Reine Rechtslehre) which aims to build a legal science that is free from political, moral, and other non-juridical influences. Through this theory, Kelsen seeks to make law a pure and objective science. According to him, the task of law is not to judge whether a law is fair or not, but to explain how a norm obtains its validity in a legal system. Therefore, the Theory of Pure Law is one of the main foundations in the development of the modern school of legal positivism and is still widely used in the study of law to this day.

In addition to the Theory of Pure Law, another important contribution is the theory of the hierarchy of legal norms or Stufenbau Theorie. Through this thought, Kelsen explained that legal norms are arranged in stages, where lower norms derive validity from higher norms8. All legal norms in this theory ultimately originate from a basic norm called Grundnorm. This concept explains why a legal system can run regularly and have legal certainty. The thought about the hierarchy of legal norms then affects many legal systems in the world, including Indonesia which applies a hierarchy of laws and regulations based on its level.

The theory developed by Hans Kelsen has a great influence on the development of modern law because it is able to explain the relationship between the validity of law and the structure of norms in a systematic manner. However, the theory has also received various criticisms. A number of experts argue that the strict separation of law from morality has the potential to ignore the substantive justice aspects that live in society. Law, in practice, not only serves to create certainty, but must also be able to realize justice and social benefits. Therefore, the debate on the relationship between law and morality is still one of the important issues in contemporary legal philosophy and the state9.

This view shows that Hans Kelsen's thinking remains relevant to understand the structure and validity of the law, but its application needs to be adjusted to the social and philosophical context of each country. In the Indonesian context, Pancasila values remain an important foundation in interpreting and developing national law so that law not only functions as a system of norms, but also as a means to realize justice oriented towards humanity and divinity.

Hans Kelsen's positivist thought began to develop in the early 20th century when Hans Kelsen introduced the Pure Theory of Law. This theory was born from a comparative analysis of various positive legal systems that form the basic concept to describe a legal community. This theory refuses to be a metaphysical study of law and seeks the basis of validity in basic norms, rather than in meta-juridical principles10. In comparison with analytical jurisprudence, Pure Legal Theory is more consistent in using its methods related to basic concepts, legal norms, legal rights, legal obligations, and the relationship between the state and the law.

Since its introduction in the 1920s, Hans Kelsen's thought began to have a great influence on the development of legal science in various countries. One of his most important contributions is the concept of a hierarchy of legal norms (steufenbau theory) which states that the legal system is a system of steps with tiered rules, where the lowest legal norm must adhere to the higher legal norm and the highest law must adhere to the most basic legal norm (grundnorm)11. This influence has made many countries systematically prepare a system of laws and regulations so as to create order and certainty in the application of the law.

Entering the middle of the 20th century, the influence of Kelsen's thought expanded as modern countries developed that required a more systematic and organized legal system. The main strength of Kelsen's legal positivism lies in its ability to provide an objective and systematic framework of legal analysis. This is especially useful in modern countries that emphasize legal certainty and procedural formality in the formation of legal norms12. In this period, Kelsen's theory was widely used to strengthen the position of the constitution as the highest legal norm that became the source of validity for all regulations under it. As a result, various countries began to develop mechanisms for monitoring laws and regulations to remain in accordance with the constitution.

At the end of the 20th century, the influence of Hans Kelsen's thought was not only seen in the field of legal theory, but Hans Kelsen also had an important role in the field of constitutional law. He was the main figure of the Constitution of the Republic of Austria in 1920 and contributed to the establishment of the Austrian Constitutional Court. His ideas about the rule of law and the importance of constitutional supervision through judicial institutions also influenced the legal system in various countries. Kelsen's thought is also one of the important foundations in the development of the concept of the rule of law which places law as the main basis in the administration of government. Through this approach, legal certainty is one of the main goals that must be realized by the state.

In countries that implement civil legal systems such as Austria, Germany, and other European countries. One of the important reasons that explains the popularity of this theory is its systematic and rational approach to law, which provides a more scientifically based alternative to previous ways of handling law that are often influenced by political, ethical, or social norm elements. In Austria, Germany, and other countries that follow the tradition of legal positivism, Pure Law Theory is considered to be in line with the demand to organize law rationally and objectively, particularly in the context of the development of a structured and hierarchical legal system.

Entering the 21st century to the present day, Hans Kelsen's thought still has a very strong influence on the development of world law. The greatest contribution of Pure Law Theory is its ability to explain hierarchical relationships in the legal system, where each legal norm derives validity from higher norms to Grundnorm as a basic norm. This approach facilitates the analysis of the relationship between norms in complex legal systems, especially in the field of constitutional law13. Although his thinking is often criticized for placing too much emphasis on formal aspects of law and paying little attention to the value of sebastive justice, the influence of pure law theory can still be found in modern legal systems that prioritize certainty, order, and consistency of legal norms. Thus, since it was first proposed in the early 20th century until today, Hans Kelsen's legal positivism has had a profound influence on the development of legal science and legal systems in the world. Hans Kelsen's intellectual legacy is still very relevant today. His theories have become the basis for the study of legal positivism, as well as applied in the analysis of laws and regulations and constitutional systems in various jurisdictions. Through his systematic and rational approach, Kelsen has laid the foundation for the understanding of law as an independent, structured, and objective science.

The most obvious implication of Kelsen's thought in Indonesia can be seen in the hierarchical structure of laws and regulations as stipulated in Law Number 12 of 2011 concerning the Formation of Laws and Regulations. The concept of Stufenbau des Rechts is manifested in the order. The 1945 Constitution is placed as the highest norm in Indonesia's positive legal system14 which functionally resembles the concept of Grundnorm in Kelsen's theory, followed by the Decrees of the People's Consultative Assembly, Laws and Regulations, Government Regulations, Presidential Regulations, and Regional Regulations. Pancasila itself is placed as a Grundnorm which is the source of legitimacy of all regulations under it. The judicial review mechanism implemented by the Constitutional Court and the Supreme Court is a concrete form of applying the theory of the Kelsen norm hierarchy in maintaining vertical consistency and legal certainty. The Constitutional Court is tasked with examining laws against the 1945 Constitution, while the Supreme Court tests regulations under the law. This practice reflects the principle of lex superior derogat legi inferior that prevails in this system is a direct reflection of Kelsen's theory of norms, where lower rules cannot conflict with higher rules15.

On the other hand, the application of Hans Kelsen's theory of pure law in Indonesia shows that there is a conceptual tension that is quite fundamental in the practice of constitutional law. The idea of a strict separation between law and morality is not fully in harmony with the plural social conditions of Indonesian society, which is characterized by the diversity of ethnicities, customs, cultures, and local values that live and develop in daily life. The contradiction between Hans Kelsen's Pure Theory of Law and the practice of law enforcement in Indonesia is clearly seen in the way that law is not only understood as a formal and autonomous system of norms, but also as an instrument for realizing substantive justice.

In Indonesia, in practice, this construction does not work absolutely, because the national legal system emphasizes a value-based approach that integrates ethics, morality, and Pancasila values in every law enforcement process16. This can be seen explicitly in every court decision which always begins with the phrase "For Justice Based on the One Godhead". An example can be found in the Constitutional Court decision Number: 46/PUU-VIII/2010 which progressively changes the construction of a child's civil relationship outside of marriage with his biological father. The decision states that a child born out of wedlock can still have a civil relationship with his biological father as long as it can be proven through scientific evidence and legal mechanisms. Prior to this decision, the positive legal construction only recognized the child's civil relationship with the mother, where the judge considered that a child born out of wedlock could not be burdened with legal consequences for the actions of his parents, so that the state has a constitutional obligation to guarantee and protect the rights of children without discrimination as stated in Article 28 B paragraph 2 of the 1945 Constitution17. This shows that the practice of constitutional justice in Indonesia is not completely tied to pure legal positivism as formulated by Hans Kelsen, the interpretation is carried out using a textual approach to the applicable norms and incorporating substantive considerations oriented towards justice, protection of children's rights, and human rights principles.

Thus, the implications of Hans Kelsen's thought in Indonesia show that there is acceptance as well as modification of the theory of legal positivism. Stufenbau des Rechts is applied in a real way in the hierarchy system of laws and regulations and norm testing mechanisms through the Constitutional Court and the Supreme Court Meanwhile, the concept of Pure Theory of Law which demands a strict separation between law and morality cannot be applied purely, because the Indonesian legal system actually integrates the values of Pancasila, morality, and the principle of substantive justice in every law enforcement process. Therefore, the legal system cannot be categorized as a completely positivistic system, because in its implementation the law does not only work within the framework of formal validity, but is also influenced by the demands of justice that live in society.