Existence as the First Act of Being

From the perspective of the existential Thomism, and following Aristotle's philosophy of being (metaphysics) as the nucleus and keystone of the whole philosophy, seeking there the most important claims of St. Thomas, the article asks the three following questions: 1) What is the novum of Thomistic metaphysics? 2) What was Thomas’ path of thinking that led him to formulate the thesis that existence is the act of being? 3) Would anyone else have discovered the uniqueness of existence if Thomas Aquinas had not done it? The answers to these questions were formulated in reference to Gilson's views and his concept of the history of philosophy and to the study of the concept of being in the texts of Thomas Aquinas and the historical sources of that concept. 1) Thomas proposed a new understanding of the structure of being, in which existence is the act that makes essence real and constitutes being's potency, together making a real individual being. Thus, Thomas formulated a new existential theory of being, overcoming the limitations of Aristotle's theory, and consistently explaining the issue related to esse (a problem that Avicenna and his followers - Parisian theologians of the 13th century- could not solve). 2) Thomas Aquinas - with the help of Avicenna's metaphysics - outdistances Aristotle's essentialism, perceiving being as composed of existence and essence. Then, examining thoroughly the proposition of the Arabian philosopher, he sees there inconsistency of attributing the position of accident to existence. According to Avicenna the element of being considered as the cause of the reality of being became - at the same time, as the accident - an unimportant component of essence. That is why Thomas Aquinas recognized that existence is the act of everything that makes essence, which transcended Avicenna's theory, and thus he formulated his own existential version of the metaphysics of being. 3) It seems that nobody else but Thomas Aquinas would have put up a thesis that existence is the first act of being because it is Thomas who did it. And what would have been if Thomas Aquinas had not done it? It is hard to say as we have no historical data to let us discuss it. Similarly, it is impossible to answer this question even assuming Gilson's thesis that the detailed claims of a given philosophy are the conclusion of the set of principles adopted at the beginning because Thomas did not have such set of principles as he modified the principles of Aristotle and Avicenna in his starting point. Would someone else have made the same modifications, thus creating a “Thomistic” set of principles? The history of philosophy analyses the things that actually happened and left their mark; it has no interest in things that did not take place and leave any trace. This could be an area for historical and philosophical fantasy, if it ever exists, but we try to stay within the field of the history of philosophy.