 Starting with Dignāga, those interested in logic started to add the particle eva to the various clauses of the three forms of reason (tri-rūpa-hetu) (Katsura 1986). Dignāga’s formulation of the three forms came in for criticism at the hands of the Nyāya thinker, Uddyotakara (c. late 6th century ce), which was, in turn, addressed by Dharmakīrti, who uses the particle to express each of the three conditions (NB 2.5).