Even though Nagarjuna's Herculean effort to provide a methodological foundation and philosophical basis for drawing together diverse Buddhist standpoints failed to achieve its aim, he gave an impulse for spiritual renewal that ramified in many directions. He founded the Madhyamika – the Middle Way – school which worked to preserve a sense of fraternity amidst diversity. With the emergence of the Madhyamika, the meta-psychological and metaphysical power of the Mahayana made an enduring impression on every aspect of Buddhist tradition. Those who resisted the suggestion that Gautama Buddha had imparted an arcane teaching to his most advanced disciples nonetheless freely borrowed Madhyamika methods and analogies to elucidate their own views. The tradition that Nagarjuna was head of the great university-monastery of Nalanda testifies to the pervasive influence of his thought. Madhyamika nurtured itself in India and then spread to China and Japan, where it flourished in conditions quite different from those of its birthplace. It came to have its own offspring – the Yogacharya school of idealism – and eventually divided into two distinct emphases. In the fifth century Bhavaviveka held that Madhyamika had a positive content of its own, whilst Buddhapalita sought to reduce all philosophical positions to absurdity in the belief that this would lead to the intuitive realization of Reality beyond all possible cognition.
Long before the Madhyamika expansion, however, Nagarjuna's vision was consolidated with consummate dialectical skill by his chief disciple, Aryadeva, one of "the four suns which illumined the world". Like his illustrious teacher, Aryadeva's life is thoroughly immersed in legend and hagiography. Biographers report that Aryadeva, born in the heart of a lotus, became the foster-son of Panchashringa, King of Sinhala, which is generally believed to be the modern Sri Lanka. His natural grace and brilliance so impressed his father that he was declared Crown prince and enthroned as heir apparent. He had already studied the Theravadin Buddhist doctrines in depth, and the prospect of becoming king saddened him. Eventually he renounced the throne for the life of a monk, but the delicate political complications arising from the presence of a former Crown prince near the throne of another successor impelled him to travel to India. Having already learnt the arts and sciences in addition to Ceylonese Buddhist thought, he sought for a teacher who could guide him to the core of the Dharma.
In time Aryadeva met Nagarjuna and became his devoted disciple for life. According to Hsuan Tsang, Aryadeva found Nagarjuna's dwelling and had himself announced. Rather than inviting Aryadeva to enter, Nagarjuna ordered that his begging bowl should be filled with clear water and taken to Aryadeva. Upon receiving the bowl, Aryadeva dropped a needle into it and sent it back. Nagarjuna welcomed the newcomer, saying to his astonished pupils that the bowl filled with water represented his knowledge, and the needle signified that Aryadeva had penetrated to its very bottom. Aryadeva was appointed the spiritual successor of Nagarjuna and eventually became head of Nalanda. He wrote a number of texts, the most famous of which is Chatuhshataka (The Hundred Treatise), which survives in the Tibetan translation and in Sanskrit fragments. Taranatha related stories that Aryadeva established monasteries and performed a number of remarkable magical feats, though he added that he could not vouch for these traditions.
Aryadeva was sometimes called Nilanetra, 'blue-eyed', because of unique markings on his face, but the name may be associated with his attainment of the 'rainbow body'. He was also called Kanadeva, 'one-eyed deva', owing to a mysterious encounter with Shiva in his aspect as Maheshvara. While disputing with theistic Shaivites, he argued that a golden statue of Maheshvara was not the god himself, and to prove the point, he tore out the left eye of the image. When Maheshvara visited Aryadeva the next day, the monk tore out his own eye to show that he was not prideful, for the statue is not the god, and the body is not the perceiver within it. Though Aryadeva's works suggest that he debated Jain philosophers, theistic Vaishnavas and Shaivites, and the followers of numerous diverse Buddhist standpoints, his concern was to remove error rather than to compel every individual to adhere to exactly the same doctrine and practice. He marshalled his sublime dialectic with special enthusiasm in critical analyses of theistic traditions in which Deity was first personalized and then absolutized. He launched equally strong critiques against Theravadin systems which emphasized practice to the exclusion of understanding.
Above all, Aryadeva wished to alter the Theravadin tendency to base spiritual practices and ethical norms on a psychological understanding of suffering, replacing it with ethical insight rooted in abstruse metaphysics. He saw that ethics without a firm grasp of metaphysics premised upon the doctrine of two truths – paramarthasatya and samvritisatya, absolute and conditional – strengthened practice while neglecting meditation. Mahayana metaphysics, on the other hand, required the marriage of meditation and ethical action like two sides of a coin. Despite the stringency of the path of emancipation, Aryadeva applied the standpoint of the Two Truths to include all receptive beings in the Dharma.
Nonetheless, relativistic explanations are useful only to the degree that they guide one towards meditation on the fullness of the seeming Void, shunyata.
Tradition holds that Aryadeva's most challenging and triumphant debate was with Matricheta, a great devotee of Maheshvara. He travelled as he taught and in time he came to Nalanda. Nagarjuna and Aryadeva were on retreat at Sri Parvata, and the monks were discomfitted by Matricheta's powerful argumentation. A message was sent to Nagarjuna, who tested his disciple and sent him to confront the threat. The four debates were conducted on two levels, dialectical and magical. Aryadeva won each dialectical exchange, but only by demonstrating his superior ability in magic through blocking Matricheta's attempts to invoke invisible assistance. Matricheta's disciples immediately entered the Sangha, but Matricheta himself held back until he had completed a profound meditation on his errors. Then he repented without reserve and eventually became a renowned Buddhist teacher. Subsequently, Aryadeva retired to South India, where he continued to teach until his death. Some sources maintained that Aryadeva was stabbed by the angry disciple of a vanquished Tirthika, yet even as he lay dying he refused to allow his followers to pursue his assailant. "Everything is unreal", he said. "Reflect upon the true meaning of all things in the world of phenomena. Who is pierced or murdered? Who is a friend and who a foe? There is neither murdered nor murderer." Thus restraining his disciples, he afforded his attacker the opportunity to escape and perhaps repent and set his feet upon the path of emancipation.
Buddhist tradition reveres Aryadeva not only as a superlative exponent of Madhyamika teachings but even more as a Bodhisattva who gave his life for the sake of humanity. He balanced uncompromisingly incisive analysis of mental confusion with positive guidance for the reorientation of consciousness towards the Bodhisattva Path. This dialectical equilibrium underlies the Chatuhshataka, Aryadeva's most honoured work. It opens with arguments for the elimination of erroneous preconceptions, namely that things are permanent, pleasant, pure or the self. The relativity of phenomenal existence and the First Noble Truth show that nothing in experience can be permanent, pleasant or truly pure. If this is understood, it is clear that there can be no self at this level. Once spiritual reliance on the mundane world is abandoned through realization of its inherent impermanence, one is ready to contemplate those Bodhisattvic practices which lead to Buddhahood. Thus one needs to eliminate the kleshas, defilements which hinder spiritual growth. To achieve this, one must seek out their cause in the many levels of enjoyment that arise from seemingly desirable objects of the senses. Only then is one ready to take up discipleship. Having made clear the requirements of the path of emancipation, Aryadeva added a vigorous analysis of the insubstantiality of all dharmas, constituents of existence, which are shown to be nothing but ciphers of shunyata. Beginning with the idea of a self, and including time, dogmatic opinions, the faculties of sense and their objects, doctrinal extremes (such as existence and non-existence, identity and difference) and conditional reality, Aryadeva subjected the elements of phenomenal existence to the negation of the Shunyavada, the way of emptiness. He concluded with a discussion of the epistemological and logical problems involved in the teaching of shunyata.
Aryadeva also composed treatises which would appeal to a wide audience of serious students. His Skhalitapramathana-yukt-hetu-siddhi (The Dialectic Which Refutes Errors Establishing Logical Reasons) sets forth a variety of erroneous views and summarizes those doctrines which will aid the disciple in overcoming them and progressing towards Enlightenment. By coming to understand the depth and tenacity of psychic structures, one prepares oneself to consider the Dharma without blindness, bias or prejudice. The metaphysical expressions of the highest truths can then be used to break up the matrices of ignorance and delusion and transform consciousness. Thus Aryadeva wrote the Dialectic to offer aid in "this world of the five degeneracies" – degenerations of life span, of understanding correct views, of afflictive emotions (greed, anger, ignorance, pride and their kin), of psychological stability of sentient beings and degeneration of this age of strife. Curiously, Aryadeva does not begin with denying the putative existence of the non-existent; rather, he affirms the existence of that which some deny. Rejecting the argument that all things come to an end and therefore need no care today, he insists that whilst all things perish, they leave seeds for future growth. Nothing just happens, but is invariably caused. Thus, only by cultivating those virtues which attack the roots of dependent causation can one achieve freedom from an endless round of involuntary rebirths.
Having affirmed the efficacy of right action because of the impermanence of all things – and not because anything can be said to remain the same – Aryadeva then denies that any conceivable notion of an individual self can be valid.
Similarly, those who are tempted to reduce the phenomenal world to some permanent material substratum are equally in error.
To those who see in the present order of things the lineaments of permanence, believing that one is naturally reborn in the same race or gender, social position or personality, Aryadeva warns:
When one begins to realize the deceptive nature of all phenomena, however, a tendency can arise through which one believes that if one only understands the nature of all the kinds of phenomena that appear, one will somehow discern the Real within them. This is the subtle error of confusing exact classification with spiritual insight.
For Aryadeva, the fundamental error in the misperception of Reality arises from a failure to recognize the egolessness or lack of inherent nature of all things. When some inherent substantiality or reality is granted to phenomena, one then fails to grasp the truth of dependent origination at its root. This misunderstanding is the direct cause of the five afflictions – desire, hatred, ignorance, arrogance and doubt – and these five ensure the relevance of the First Noble Truth. Metaphysically, the error can be explained with relative ease, but it cannot be understood without great effort. To grasp the voidness of the seeming full and the reality of the seeming void, one has to penetrate and break up the patterns of misperception and misunderstanding that pervade every level of embodied consciousness. Thus the pure metaphysics of the Shunyavada – way of the Void – must be translated into the Madhyamika, the Middle Way, which avoids all extremes and excess. The Bodhisattva Path, along which one journeys by stages through progressive awakenings to the real nature of things and the gradual stripping away of false conceptions of the self, is the only way to perfect knowledge and full Enlightenment. The Middle Way, which has been characterized as 'zerology' – the study and practice of shunya – is trod by penetrating learning and also reducing oneself to a zero while joining oneself to the whole – shunyata – through selfless service and meditation on fundamentals. Aryadeva is called a Bodhisattva because he fused clarity of insight with compassionate action in the unwavering conviction that all could tread the path of emancipation.