The subject of this research is the advantage of the ontology of process over the ontology of substance in description of the ontological structure of the world. Analysis is conducted on the comparative heuristic potential of essentialism and substantialism on the one hand, and philosophy of the process on the other hand. Essentialism postulates stable, mature, already constituted objects with objectively given essential characteristics that form profound structure of the object. The clearly differentiated array of concepts and categories that reflects the structure of reality and the nature of things is placed on the reality in the flow of becoming. The philosophy of process, in turn, insists on the dynamic and relational nature of reality, and considers time to be the factor constitutive of reality. The fabric of reality is comprised of the processes that relate and interact with other processes forming their dynamic context. The article demonstrates the applicability of the ontology of process in biology, namely on the example of the phenomenon of symbiosis and holobionts. The arguments are provided that the object can be ontologically described as a process; however, a range of processes (for example, photosynthesis) cannot be analyzed in the object categories. Criticism is expressed towards the concept of essential properties of the substance, taking into account perspectivism and variants of the processes of with objects. It is indicated that gradualism characteristics to the philosophy of process allows removing dichotomies and introducing nuances into the binary picture of reality. The novelty of this work consists in highlighting the questions faced by the philosophy of process, namely the question of determination of the status of time essential for determining the process as the basic ontological entity.