本文從佛教興起的背景探討初期佛教梵行思想的時代意義。首先論述在佛陀時代，奧義書的世界觀如何為不同的「順世論」(lokāyata)所加詆毀、終結、而取代之，以及這些順世論的觀點如何危及後奧義書時代的宗教道德論述的基礎。文中明白指出順世論者的共同特點乃是否定人要對其行動結果加以負責。這些否定行動及道德行為意義的論者可謂「倫理學上之虛無主義者」，其主張顯示出沙門時代在道德推理(moral resoning)上所面臨的思想困境。準此而言，初期佛教對於人的行動預設三大要件，即業、作用及精進(kamma, kiriya, viriya)，有其重大的意義。而梵行做為一種精進行為，是構成行動的最後要件。文章接著鋪陳初期佛教有關業、作用即精進的思想，並與當時其他宗派--特別是尼乾陀若提子(Nigantha Nātaputta)--的教義加以比較。最後探討為何「倫理學上之虛無主義者」之教義被阿難稱為「非梵行」(abrahmacariya)，以及阿難稱尼乾陀若提子及其他一些宗教師的教法為「不安之梵行」(anassāsika brahmacariya)（亦即修苦行無法造福）之用意何在。This paper is an exploration of the early Buddhist understanding of brahmacariya in the context of the intellectual climate at the time of the Buddha. I endeavor to demonstrate how the Upanisadic worldview is undermined and eventually superseded by different “materialist” worldviews and how the ethical discourse of the Post-Upanisadic age is threatened by these materialists’ views. I point out that one of the common features of these views is the denial of the performance and consequence of action. This denial of the existence of action and the ethical conduct by the dominant “ethical nihilists” (as we shall call them) then create a predicament for moral reasoning. In this regard Buddhist theory holds that there are three components of action: kamma, kiriya and viriya. According to the Buddha, practicing brahmacariya is a viriya (effort, exertion), the last component of action. Hence, in order to argue for the ontological significance of brahmacariya, the Buddha has to offer convincing explanations of all three components—kamma, kiriya and viriya. I therefore explore the early Buddhist notions of kamma, kiriya and viriya at length by comparing them with the teachings of other religious teachers especially Nigantha Nataputta. I conclude by discussing how Ananda labels the teaching of the Nigantha Nataputta and others as anassasika brahmacariya (the discomforting brahmacariya); that is, as harsh austerity which is unable to give blessing.