本文先以奧古斯丁對時間的真實性的置疑開始，探討時間的本體論地位，即所謂時間的外延性問題，在康德的《純粹理性批判》如何處理。本文先討論康德的「超越感知論」，指出時間在這裡只是一種形式多於一種實質的存在，然後在「圖象論」「經驗的比喻」裡面所謂「恆存的實體」(substance) 的假設，雖然有某程度的外延性，但這個概念本身有很多矛盾和吊詭，而本身也是經驗可能的假設，不能落實到具體的存在。本文的核心部份要指出，在康德裡，時間的真實性，必須建立在所謂「超驗想像力」之上，而跟隨海德格的解釋，「超驗想像力」可以在瞬間的直觀裡構成圖像，而這個過程必然有時間的參與。本文順著這個線索，從康德在「先驗感性論」裡對時間基本結構的陳述，尤其所謂「共時性」和「歷時性」兩個基本形式，推論任何時空實際經驗，必須在這兩者的參與，以至模塑經驗的方式，缺一不可，而一旦有兩者的參與，時間的真實性必然建基在認知單位的構成、以至知識的可能性之上。

This paper begins with the skepticism about the ontological reality of time raised by Augustine, which centers around the problem of the extension of time, and will see how it is dealt with in Kant’s Critique of Pure Reason. It first examines the treatment of time in “Transcendental Aesthetics”, in which time is merely a formal condition for experience. Then the second “analogies of experience”, namely the “permanence of substance”, in the schematism chapter, it has certain meaning of extension but is itself a paradoxical concept and cannot go beyond the mere assumption for possible experience. The central argument of this article is that the reality of time may be found in Kant’s “transcendental imagination” and its distinction from “reproductive imagination” and their relation with “empirical law”. It follows two hints provided by Heidegger, who argues that “transcendental imagination” provides a “free space” (Spielraum) or “open horizon” (offener Horizont) for other “reproductive imagination”, and that in every moment of intuition, time has already taken part in the formation of a given picture. It then draws from Kant’s description of time in his “transcendental aesthetics”, namely “succession” and “simultaneity”, and argues that in every experience about appearance, both of these must take part in the formation of experience. It concludes that the reality of time can be understood by Kant from the possibility if the formation of units for perception and knowledge.