為什麼「在者」在，而「無」反而不在？出於對傳統形而上學之深刻的不滿，海德格爾對存在發起徹底的追問。故此，對「無」的長久運思也成了他畢其一生之志業。而這種運思方向亦使其有了與古典時代強調證量體悟的東方聖哲握手言歡的可能。但他自身所努力營建的形上學體系仍留有不少的模糊地帶，故我們試著藉其所展開的視野，與印度的《奧義書》和漢語《道德經》加以互勘比較，發現「無」成了他們共同的存在圖景。而說穿了，純粹的有與純粹的無是一回事。此語早被老黑格爾所揭出，本文的比較，即基於東西方不同的哲學思想對以「無」為核心的存在圖景之探討，以期獲得一個較清晰的對「無」的呈現。

Why is ”being” present but ”non-being” not present? Out of deep dissatisfaction with traditional metaphysics, Martin Heidegger made radical questions about being. Therefore, the contemplation about ”non-being” became his lifelong career, and such contemplation makes it possible for him to relate to the oriental sages who stressed pratyaksa. However, the metaphysical framework he himself built is still somewhat blurred; therefore, we compare his insights with ”Upanishad” and ”Tao Te Ching” and find out that non-being is the vision he shared with the oriental sages. Ultimately, pure being and pure non-being are one and the same, which had already been revealed by Hegel. The comparison we make in this article is based on the existential visions of oriental and occidental philosophies about non-being in wishes to present ”non-being” more clearly.