本文主要探討《佛說不增不減經（Anunatvqpurnatva-nirdewa）》「眾生界不增不減」的修學義理；至於落實的辦法，則以眾生界、法界、法身、如來藏等關鍵字詞為環節，闡發眾生界之所以不增不減在理路的根據與開展。 如果僅就粗淺的經驗所及，通常大致傾向於認為，在時間之流的沖刷下，一定範圍內的眾生數目，要不是增多，就是出現減少的情形，也就是說，幾乎不可能維持在零增加且零減少的水平。然而，《不增不減經》不僅拒絕接受表面上看似有增有減之見解，而且擺明了就在經典的標題，高高掛出眾生界「不增不減」為其主旨。本文扣緊既是《不增不減經》的主旨也是本文主題所關注的「眾生界不增不減」，沿著關鍵字詞，逐一打開其間之意涵、根據、和理路。在論述架構上，總共分成五節。第一節，「緒論」，就論文的構成項目，由研究主題到研究目標，逐一交代全文的構想與梗概。第二節，切入經典主旨——「眾生界不增不減」——並且就其義理構成，透過系列的提問，展開深度的解析。第三節，切換到「法界」，論陳此一關鍵字詞如何一方面使經典主旨得到確證，另一方面又使經典在論述的觸角和理路都獲得重大的拓展。第四節，進一步切換到「法身」，透過此一關鍵字詞，論陳經典主旨如何漸次延伸且一一貫穿眾生、聲聞、緣覺、菩薩、和如來等生命形態和佛法修學專業的身分，不僅出之於一貫的著眼點，統整地述說各式各樣的生命形態和佛法修學專業的身分何以分別造成，而且面對生命相續形形色色的差異，恰好成全經典主旨的甚深義。第五節，「結論與展望」，總結全文要點，並且針對後續相關的研究，預做前瞻。 本文採取的研究進路，以佛法的修學為著眼點，爬梳與闡明經典在修學所展開的理路，由此形成對修學義理的一份理解。至於預期達成的目標，以如下三點最為首要。第一，對《不增不減經》，做出相當完整的鑽研。第二，以經典主旨和關鍵字詞打通《不增不減經》的理路，凸顯整篇經文在義理上的整全性與連貫性。第三，直接藉由《不增不減經》的鑽研，以接近原汁原味的內涵，開啟生命哲學的一扇門窗，並且認識法界、法身、如來藏等概念所可能指向的理趣。

The present study examines Buddhist doctrine of "neither increase nor decrease in the realm of sentient beings" in the Anunatvqpurnatva-nirdewa in terms of a doctrinal development focusing attention on keywords from the realm of sentient beings (sattva-dhatu), dharma-dhatu, dharma-kaya, to tathagata-garbha. The Mahayana has sometimes been associated with the doctrine that there is neither increase nor decrease in the realm of sentient beings, a doctrine which is often linked to the Prajbaparamita-Sutras or the Madhyamika school. In this paper, I look into just such a doctrine, as it is found in a Chinese traslation of the Anunatvqpurnatva-nirdewa, a Buddhist scripture translated by Bodhiruci in 525. Several passages of this scripture were cited in the Ratna-gotra-vibhaga, a treatise still preserved in Sanskrit, Chinese and Tibetan, and give us textual sources for research into the Chinese translation of this scripture. In the Anunatvqpurnatva-nirdewa, the very way in which the doctrine of neither increase nor decrease in the realm of sentient beings is defined and verified through the employment of the dharma-dhatu thoery, a theory which, in turn, is verified by reference to theories of dharma-kaya and tathagata-garbha. So in order to understand this scripture's discursive construction of the doctrine of neither increase nor decrease in the realm of sentient beings, we must explore its conception of such keywords as dharma-dhatu, dharma-kaya, and tathagata-garbha. It is my hope that an examination of such a scripture with the focus on the doctrine of neither increase nor decrease in the realm of sentient beings may contribute to the study of the various ways in which the contours of the Mahayana have been drawn from a doctrinal perspective.