Abstract

Time is not only a dimension of the physical world but also a construct of the mind. Existential Realism (ER) offers a present-centered ontology of time, distinguishing existence (what concretely exists now) from reality (the wider web of past and future events that have effects or significance without presently existing) – a “two-tiered” view of temporal being. In brief, ER holds that only the present moment and its contents exist in the full ontological sense, yet reality extends beyond the present: past events and future outcomes do not exist now, but are nonetheless real insofar as they left traces, continue to exert causal influence, or shape well-founded anticipation. This framework reconciles the humility of acknowledging that we directly observe only the present with a robust realism about the world’s structure across time. Prior work in ER has explored how adult brains represent time (memory, anticipation) in line with this ontology, and how cognitive science views time as an actively constructed experience. However, an important question remains underexplored: how does this ontological understanding emerge during childhood? In this paper, we align Piagetian developmental psychology with ER’s metaphysical framework to trace the ontogeny of temporal and ontological understanding. We argue that the child’s mind initially collapses reality into the present – effectively conflating “real” with “now” – and gradually migrates toward a higher-tier temporal realism that mirrors ER’s distinction between existence and reality. The developmental journey from infantile presentism to a mature understanding of time will be outlined through constructivist stages, using ER’s terminology of tiers, collapse, transition, and constructed present to describe the child’s evolving temporal framework. By mapping cognitive development onto ER’s structure of time, we gain insight into how the mind builds a layered reality from the immediate constructed present to an extended timeline. We also identify key markers – the emergence of tense in language, understanding of object permanence and enduring objects, and use of counterfactuals – as evidence of ontological tier transitions in childhood. Finally, we conclude with implications of this developmental perspective for education, introspective self-modeling, and understanding temporal pathologies in cognition.