Theravāda
The elder school — the original teaching preserved in Pali. The Buddha's first discourse in the Deer Park at Sarnath: the Four Noble Truths, the Eightfold Path, the Middle Way between asceticism and indulgence. No cosmological hierarchy, no mandalas, no initiatory transmission. Only the precise investigation of experience: what is suffering, where does it arise, can it cease, what is the path to cessation. The foundation that all later Buddhist schools either build upon or react against.
Avidya (Sanskrit) or avijja (Pali) is the first nidana in the twelvefold chain of pratityasamutpada as taught in the Nidana Samyutta of the Samyutta Nikaya: from avidya arise samskaras (volitional formations), from samskaras vijñana (consciousness), cascading through nama-rupa, sadayatana, sparsa, vedana, trishna, upadana, bhava, jati, and finally jara-marana — the entire structure of samsaric existence. Avidya is technically defined as the fourfold viparyasa (cognitive inversion): perceiving the anitya (impermanent) as nitya, dukkha as sukha, anatman as atman, and the asubha (impure) as subha. Nagarjuna's Mulamadhyamakakarika reframes avidya as the failure to see pratityasamutpada itself — ignorance is not merely a wrong belief but the reification of svabhava where none exists.
Tanha (Pali) or trishna (Sanskrit) is identified in the Dhammacakkappavattana Sutta — the Buddha's first discourse at Sarnath — as the samudaya (origin) of dukkha, constituting the Second Noble Truth. The Pali canon distinguishes three species: kama-tanha (craving for sensory gratification), bhava-tanha (craving for continued existence), and vibhava-tanha (craving for annihilation). Within the twelve nidanas of pratityasamutpada as recorded in the Samyutta Nikaya, tanha occupies the eighth position, arising conditioned by vedana (feeling) — it is the precise hinge-point where the chain can be broken, because between vedana and tanha lies the gap where sati (mindfulness) can intervene before compulsive reactivity solidifies into upadana (clinging).
Dukkha is the First Noble Truth (dukkha ariya sacca) as proclaimed in the Dhammacakkappavattana Sutta at the Deer Park in Isipatana. The Pali tradition distinguishes three registers: dukkha-dukkha (the suffering intrinsic to painful experience), viparinama-dukkha (the suffering inherent in the impermanence of pleasant states), and sankhara-dukkha (the pervasive unsatisfactoriness of all conditioned phenomena composed of the five aggregates — rupa, vedana, sañña, sankhara, and viññana). The Visuddhimagga identifies dukkha as one of the tilakkhana (three marks of existence) alongside anicca and anatta, specifying that its full comprehension (pariñña) through vipassana practice constitutes the first of four functions the noble truths demand: dukkha is to be fully understood, not merely endured or escaped.
The Majjhima Patipada (Middle Way) was proclaimed in the Buddha's first discourse, the Dhammacakkappavattana Sutta, as the path between the extremes of kama-sukhallikānuyoga (devotion to sensual pleasure) and atta-kilamathanuyoga (devotion to self-mortification). Nagarjuna's Madhyamaka school elevated this to an ontological principle: the Middle Way between sasvatavada (eternalism, the view that things possess svabhava) and ucchedavada (nihilism, the denial of conventional causation). The Mulamadhyamakakarika demonstrates that pratityasamutpada itself is the Middle Way — neither asserting nor denying existence, but revealing that all dharmas are empty of inherent nature while functioning perfectly at the level of samvriti-satya (conventional truth). Candrakirti's Madhyamakavatara further systematizes this as the integration of the two truths (satya-dvaya) without collapsing either into the other.
Anicca (Pali) or anitya (Sanskrit) is the first of the tilakkhana (three marks of existence) alongside dukkha and anatta, pervading every samskrta (conditioned) dharma without exception. The Visuddhimagga of Buddhaghosa maps the progressive insight into impermanence through the ñana (knowledges) of the vipassana sequence: from udayabbaya-ñana (knowledge of arising and passing) through bhanga-ñana (knowledge of dissolution), where the meditator perceives the kshana (momentary) arising and ceasing of all nama-rupa at increasingly fine temporal resolution. The Anguttara Nikaya records the Buddha's declaration that 'sabbe sankhara anicca' — all formations are impermanent — and the Mahaparinibbana Sutta preserves his final words: 'vayadhamma sankhara, appamadena sampadetha' (all conditioned things are subject to decay; strive with diligence). In the Abhidhamma analysis, each dhamma exists for only a single thought-moment (cittakkhana) before giving way to its successor.