The aim of this chapter is to highlight the centrality of what Heidegger calls the ‘ontological diff erence’ to our understanding of the twofold of existence: individuality and interaction. This diff erence is, in Dewey’s terms, between aesthetic and refl ective experience, but Dewey did not fully comprehend it because he approached it primarily from a pragmatic perspective in refl ective experience. Peirce helps here, as he describes the unity inherent to existence as individuality, thereby distinguishing it more clearly from interaction. For Heidegger, the ontological diff erence marks the diff erence between being and beings; between the simple and the multiple; between two diff erent ways of questioning being (the grounding question and the guiding question); between originary and ordinary senses of time; between meditative and calculative thinking. Comprehending the ontological diff erence in this way, within existence or secondness, also distinguishes it from the logical diff erence (between secondness and thirdness) and Ereignis (between fi rstness and secondness). In this chapter we also discuss the character of Ereignis, which is unlike either the ontological diff erence or the logical diff erence. Each of these three, marking folds in experience, is unique.