Fakhr al-Din al-Razi (1149–1210) was one of the most innovative and influential thinkers in the first stage of what is sometimes called “post-classical” Islamic thought. Along with other major thinkers of the Islamic East in the twelfth century, notably Abu l-Barakat al-Baghdadi and al-Suhrawardi, Fakhr al-Din reacted critically to the philosophy of Ibn Sina. He produced a voluminous corpus that is often elusive in terms of conveying Fakhr al-Din’s own considered opinions, but is packed with subtle philosophical argumentation on pretty well every aspect of Ibn Sīnā’s thought. Fakhr al-Din did also stake out distinctive positions of his own, for example with respect to the problem of providing real definitions, the distinction between essence and existence, the principles of physics, the unity of the human soul, and the source of ethical norms. This abundant output in philosophy was only one part of his life’s work, which includes texts on Islamic law, theology, astrology, and one of history’s most important commentaries on the Quran. The authors of this article focus on understanding the problem of being in the teachings of Fakhr al-Din Muhammad al-Razi, one of the main participants in the movement of freethinkers in Islam. Fakhr al-Din al-Razi as a representative of intellectual Salafism offers alternative solutions to the views on the existence of the ancient Greek philosophers Aristotle, Democritus, Heraclitus, Epicurus and the Eastern thinkers Farabi, Ibn Sina, Abu Suhail Masihi. This article provides arguments based on Razi’s work on an ontology that was unique to his time. In particular, in his study, N. Naimov cites Razi’s sharp thoughts about being, existence, and the creator of the universe in Chahordoh risola (Fourteen treatises). On the other hand, we can see the opposite in Razi’s writings on Islamic theology. When analyzing Razi's position, we drew conclusions using the methods of scientific knowledge, such as comparative analysis, analysis and synthesis, logic, historicity, his works and data from various researchers. It is known that Razi is one of the free-thinking and advanced thinkers-philosophers of the Middle Ages, who played a large role in the development of the advanced philosophical thought of the peoples of the Near and Middle East, as well as one of the thinkers who had a significant positive impact on the worldview of several later thinkers-philosophers of Central Asia and Muslim East.