In George Santayana’s work, “The Life of Reason: The Phases of Human Progress,” the term "existential" is employed to distinguish between different aspects of reality and experience. For instance, Santayana contrasts the physical with the existential, noting that certain unities are functional rather than tangible ([1]). He also uses the term to underscore the necessity of identifying fundamental reality elements—such as their number and affinities—before any meaningful analysis can proceed ([2]). Furthermore, he highlights the immediacy of experience as a primary form of reality while still allowing for an ideal or conceptual dimension ([3]). Lastly, Santayana points out that even mental facts contain an existential element that links more closely to material existence than traditional dualist views, such as those proposed by Descartes, would suggest ([4]).