The Eighteen Exclusive Buddha-Qualities Begin

T1606 lists all eighteen by name, as recorded in scripture: the Tathāgata has no accidental error, no sudden or inappropriate outburst, no lapse of memory, no unsettled mind, no perception of things as inherently different, no equanimity lacking careful discernment; his aspiration never declines, his diligence never declines, his mindfulness never declines, his concentration never declines, his wisdom never declines, his liberation never declines; every bodily act, every verbal act, and every mental act is led by wisdom and proceeds in accordance with wisdom; and he knows the past, the future, and the present each without attachment and without hindrance.

T1606 explains each of these first six by direct contrast with an arhat, who, though free of affliction, may still retain certain small residual patterns a buddha never exhibits at all.

No accidental error: an arhat who has already exhausted the contaminants may still, while walking to town to beg for alms, find themselves keeping company with a dangerous elephant, horse, ox, or dog; treading through thorny brush or leaping over a ditch when a smoother path was available; speaking to a woman in her home in a manner not fully considered; or wandering from a proper road onto some improper byway through the wilderness, perhaps even in the company of bandits or fierce beasts. Such small missteps, T1606 notes, can still occur for an arhat — but never for the Tathāgata.

No sudden or inappropriate outburst: an arhat may, wandering lost in the wilderness or entering an empty dwelling, cry out loudly or otherwise make a sudden, startling noise, or — through the lingering, non-afflictive residue of past habit — bare the teeth and lips in an unrestrained burst of laughter. The Tathāgata never does.

No lapse of memory: an arhat may still, through a non-afflictive residue of habit, forget something done or said long ago. The Tathāgata never forgets.

No unsettled mind: an arhat's mind becomes concentrated only once deliberately gathered, and reverts to an unconcentrated state the moment that gathering ends. The Tathāgata's mind is never, at any time, in an unconcentrated state.

No perception of things as inherently different: an arhat still perceives the ongoing cycle of birth and death as something to be resisted and nirvāṇa without remainder as something genuinely still — a residual perception of contrast between the two. The Tathāgata perceives no such difference between saṃsāra and nirvāṇa at all, abiding instead in the very highest form of great equanimity.

No equanimity lacking careful discernment: an arhat may, at times, forgo some specific opportunity to benefit sentient beings without having carefully weighed, through wisdom, whether that opportunity was genuinely worth pursuing. The Tathāgata never abandons any such opportunity without first discerning it fully — nothing is ever simply let go of by default.

T1606 also maps these six onto the treatise's own threefold division: no accidental error rests on purity of bodily conduct; no sudden outburst rests on purity of verbal conduct; and the remaining four — no lapse of memory, no unsettled mind, no perception of things as inherently different, and no equanimity lacking discernment — together rest on purity of mental conduct.