Nāgārjuna's other signal contribution is the doctrine of the two truths. He argues: truth appears on two levels. Conventional truth (saṃvṛtisatya)—in daily life, the world seems to 'exist,' and that existence serves well enough to conduct our affairs; we speak of 'chariot,' we speak of 'person,' we say 'I'—these work practically, even though ultimate analysis cannot sustain them. And ultimate truth (paramārthasatya)—when we look deeply, all things are empty; nothing possesses intrinsic being. Neglect either truth, and the Buddha's teaching eludes us—cling only to conventional truth and you are snared in eternalism; cling only to ultimate truth and you fall into nihilism. This middle path remains faithful to Buddhist principle: emptiness is not the source of the world (as Brahman is the source in Vedānta); emptiness is simply the inexplicable groundlessness of all conception and existence—a groundlessness bearing no generative or creative relation to the world.
Asaṅga and Vasubandhu: Yogācāra and Ālayavijñāna
Asaṅga and Vasubandhu (c. fourth century)—two brothers who founded the second great Mahāyāna school of Buddhist philosophy—advanced one step further with their doctrine of vijñaptimātra, 'Consciousness Only.' Vijñaptimātra means precisely that: all that we see, hear, feel, and experience is the mind's own projection; no distinct reality exists outside consciousness. Here they have moved somewhat from Buddhist orthodoxy—for they grant that beneath all visible reality lies a positive entity. For the Yogācāra school, this supreme reality is ālayavijñāna (ālayavijñāna)—literally 'storehouse-consciousness' or 'warehouse-consciousness.' It contains the seeds of all experience—just as countless seeds lie dormant in a warehouse and sprout when conditions align, so too the seeds of all actions lie gathered in the storehouse-consciousness, bearing fruit when circumstances permit. This conception draws perilously close to the Vedāntic notion of Brahman.
Yet they did not drift into the old Vedāntic current by declaring this entity identical with the world—the relation is defined as 'neither different nor identical,' a cautious, liminal position. In later East Asian Buddhist thought (especially in the Awakening of Faith in the Mahāyāna, a text of disputed authorship and date yet of immeasurable influence), this conception was carried further—an undivided supreme consciousness is posited as the ground of the manifold world. This 'one mind' has two aspects: the absolute aspect (tathāgatagarbha—which is pure, unchanging) and the phenomenal aspect (ālayavijñāna—which is deluded, mutable). Yet it is never said that the world is an 'unfoldment' or 'manifestation' of that absolute reality (as in Vedānta, where the world emerges from Brahman); rather, the world's suffering and craving are traced to worldly delusion—that is, the world is not a creation of the absolute reality, but a misunderstanding of it.
Tathāgatagarbha: The Most Contested Bridge
The most contested notion in Mahāyāna Buddhism is tathāgatagarbha. 'Tathāgata' means Buddha—he who 'thus has gone' or 'thus has come' (the Sanskrit term admits both readings). 'Garbha' carries many meanings—womb, essence, embryo, seed, storehouse. Thus tathāgatagarbha can mean 'the womb of the Buddha' (wherein Buddhahood lies hidden), or 'Buddha-nature' (the latent Buddhahood inherent in each being), or 'the seed of Buddhahood.'
The Tathāgatagarbha Sūtra of the third century and the Śrīmālādevī Siṃhanāda Sūtra proclaim: in all sentient beings, the seed of Buddhahood lies dormant—veiled beneath afflictions (kleśa: mental impurities—craving, hatred, delusion, and the rest). The sūtras offer nine similes, the two most celebrated being these: as a golden image wrapped in filthy cloth—the image is gold indeed; one need only remove the dirt; as a lotus blossom enclosed in mud—the flower is already formed within; one need only break through the husk and emerge.