懷海德(Alfred North Whith Whitechead 1861-1947)可說是二十世紀西方最偉大的形上家；當形上學成為眾矢之的之際，懷海德和極其少數的哲學家卻仍堅持形上學的哲學價值。這使他在當代哲學與後現代哲學價值。這使他在當代哲學與後現代哲學中卓然獨立，開啟了嶄新的研究方向。其實懷海德開始並不是一位哲學家，他的思想發展經歷了三個階段：一是數學與邏輯階段，二是自然科學詧學或本體論與認識論階段，三是思辨哲學或宇宙論時期，這最後的階段便是他形上學發展的成熟階段。早在自然哲學時期，懷海德雖已肯定形上學的價值，認為科學的研究不能稍減我們對形上學的需求。而有關可能性與實現性之間的關係，尤其有賴於形上學的研究，科學甚至使得形學的需求更為迫切。但在個階段，他也曾明確地區隔自然哲學與形上學的不同。他指出形上學主要在精確地說明指證宇宙際的經驗，其來源與類型，而科學則在透過納邏輯，以特定概念來組織知覺經驗，進而找出自然的法則。前者涉及知學者與被知覺物，而後者僅涉及知覺經驗，雖然兩者都以「立即經驗」為出發點，但各走各的路，可以說是同途而殊歸。但到了思辨哲學時期，懷海德再次肯定形上學的重要性，進而發展出「歷程宇宙論」的形上系統。本文試就四方面說明其核心理論：一是以「現行單元「為基礎的「多元實在論」(pluralistic realism)；二是以「攝持」和以「上帝」為基礎的「哲學有神論」(philosophical theism)。

Alfred North Whitehead was one of the greatest metaphysicians in the twentieth century of the western world. He and a very few others insist in exploring the philosophical value of metaphysics, which has been cast in great doubt by the modern schools, ranging from positivism, historicism, psychologism, socialism, to logicism, whitehead’s strong commitment to metaphysics and his philosophy of organism had given the impetus to the rise of process philosophy/theology in the United States, which was considered a form of constructive postmodernism. However, at the beginning whitehead was not a philosopher; the development of his thought has at least undergone three stages: (1) the mathematical and logical stage, (2) the ontological and epistemological stage or the stage of nature philosophy, (3) the stage of speculative philosophy and cosmology, and the last stage shows the culmination of the development of his metaphysics. As a matter of fact, as early as at the stage of nature philosophy Whitehead has shown his deep concern with metaphysics which he considers to be of tantamount importance as nature philosophy that cannot be reduced by the studies of natural sciences. Science may even render the metaphysical need more urgent for it can deal with the relation between possibility and actuality, which is necessary for some scientific research. Nevertheless, at this stage whitehead has also made metaphysics distinguished form science; as the former aims at giving precise elucidation of every source and every type of experience that yields demonstrative proof of the reality and of its nature, whereas the latter only need to deal with sense perceptions. Thus Whitehead says that the basis of science does not depend on the assumption of any of the conclusions of metaphysics, though both of them start from the same given groundwork of immediate experience. Finally, at the last stage of his philosophical development, Whitehead undertakes constructing a metaphysical system of tremendous complexity. The present paper is an attempt to understand Whitehead’s metaphysics form four aspects: (1) to understand it as a pluralistic realism with respect to his doctrine of actual entities; (2) to understand it as a pan-experientialism with respect to his doctrine of pretension; (3) to understand it as a theory of value with respect to his doctrine of eternal objects, and (4) to understand its as a philosophical theism with respect to his doctrine of God.