Although the ideas in Process and Reality are well-recognized by many scientists in various disciplines beyond philosophy, these investigations are focused on the formal interpretation of the notion of space in the context of mereotopology. Indeed, the notion of time is either neglected completely or understood as an abstraction from the four-dimensional existence of enduring objects. However, there is no elucidation of the notion of time beyond this existence. We introduce a monadic second order language to formalize the ultimate principles (...) presupposed to Whitehead’s investigation, i.e., creativity, novelty and advance have been analyzed and reformulated as axioms. The models of the formulated theory are linear process structures, which are a special type of occurrence structures. The model-theoretic aspects of their theory are discussed in the present paper. Our fundamental theorem indicates that the worlds, which ground the knowledge of actual occasions, are ordered linearly and are equal for contemporaneous actual occasions, which implies a condition essential to the being of time. (shrink)