  The ontological emphasis that Heidegger places on temporality might usefully be seen as an echo and development of Kant's claim that embeddedness in time is a precondition for things to appear to us the way they do. (According to Kant, embeddedness in time is co-determinative of our experience, along with embeddedness in space. See above for Heidegger's problematic analysis of the relationship between spatiality and temporality.) With the Kantian roots of Heidegger's treatment of time acknowledged, it must be registered immediately that, in Heidegger's hands, the notion of temporality receives a distinctive twist. Heidegger is concerned not with clock-time (an infinite series of self-contained nows laid out in an ordering of past, present and future) or with time as some sort of relativistic phenomenon that would satisfy the physicist. Time thought of in either of these ways is a present-at-hand phenomenon, and that means that it cannot characterize the temporality that is an internal feature of Dasein's existential constitution, the existential temporality that structures intelligibility (taking-as). As he puts it in his History of the Concept of Time (a 1925 lecture course): “Not ‘time is’, but ‘Dasein qua time temporalizes its Being’ ” (319). To make sense of this temporalizing, Heidegger introduces the technical term ecstases. Ecstases are phenomena that stand out from an underlying unity. (He later reinterprets ecstases as horizons, in the sense of what limits, surrounds or encloses, and in so doing discloses or makes available.) According to Heidegger, temporality is a unity against which past, present and future stand out as ecstases while remaining essentially interlocked. The importance of this idea is that it frees the phenomenologist from thinking of past, present and future as sequentially ordered groupings of distinct events. Thus: