The Abhidhamma identifies two ultimate realities: phenomena (dhamma) and Nirvana.
The Abhidhamma, the Buddhist scholastic tradition preserved primarily in the Pali Canon, distinguishes between two categories of ultimate reality (paramattha-sacca). These are phenomena and Nirvana. This framework appears most explicitly in the Abhidhamma Pitaka texts, particularly the Dhammasangani (Enumeration of Phenomena), which opens by categorizing all experience into either conditioned things (sankhata dhamma) or the unconditioned (asankhata dhamma).
The term "ultimate reality" here means something that exists by its own nature and cannot be reduced further through analysis. This contrasts with conventional realities (sammati-sacca), which are conceptual designations we apply to collections of more fundamental elements.
Phenomena, or dhamma, constitute the first ultimate reality. The Abhidhamma analyzes experience into irreducible components: mental factors (cetasika), consciousness (citta), material form (rupa), and Nirvana. These are ultimate because they possess their own intrinsic nature (sabhava) independent of conceptual designation.
Mental and material elements are further subdivided into many categories. The Dhammasangani lists consciousness, mental factors associated with it (like feeling, perception, volition), and material properties. These elements arise in causal relationships according to dependent origination and are constantly arising and passing away. Despite their impermanence, they are still considered ultimate realities because they genuinely exist as functioning entities until they cease.
Nirvana (also spelled Nibbana in Pali) is the second ultimate reality. Unlike conditioned phenomena that arise and pass away, Nirvana is explicitly unconditioned (asankhata) and permanent. It is not produced by causes and conditions, but rather represents the cessation of all conditioned phenomena and the extinguishing of craving, hatred, and delusion.
The Abhidhamma texts treat Nirvana as something that genuinely exists and can be directly experienced, particularly through the fourth noble truth—the path leading to cessation. This distinguishes the Abhidhamma view from the position that Nirvana is merely the absence of something. For the Abhidhamma, it is a positive reality, though one beyond sensory experience and conceptual construction.
The Abhidhamma reduces all reality to these two categories because they represent a fundamental division: the conditioned realm of experience that operates according to cause and effect, and the unconditioned peace that transcends that cycle. Everything that has a cause and arises in dependence on conditions falls into the first category. Everything that is permanent and beyond the conditioning process falls into the second.
This framework allows the Abhidhamma to explain both the structure of samsara (cyclic existence) and the possibility of liberation. All ordinary experience involves phenomena, but awakening involves penetrating the nature of conditioned phenomena and realizing the unconditioned reality of Nirvana.
The Mahayana Buddhist traditions, including the Sanskrit Abhidharma schools, developed somewhat different metaphysical frameworks. The Yogachara school emphasized consciousness and mental construction, while the Madhyamaka school taught that ultimate reality transcends all conceptual categories. However, the Theravada Abhidhamma's two-part scheme remains the clearest and most systematic early Buddhist answer to this question.
The Tibetan Buddhist philosophical schools preserve detailed commentaries on both Pali and Sanskrit Abhidharma traditions, and they maintain similar fundamental distinctions between conditioned and unconditioned phenomena, though with varying interpretations about the ultimate nature of emptiness and consciousness.