Determination
There are two ways of determining an object or a fact: positive determination (Wyl. yongs gcod) and negative determination (Wyl. rnam bcad). Negative determination is a process where ‘the nature of a thing is known [indirectly] through the elimination of what are not the thing’ and positive determination is where ‘the nature of a thing is [directly] affirmed and by doing so, what are not the thing are eliminated’.[1]
In the case of a vase, for example, yongs gcod would be the determination that the vase is impermanent. rnam bcad would be the determination that the vase is not permanent. In the context of the rope-seen-as-a-snake example, the negation of the rope's being a snake is a rnam bcad. The affirmation of the rope's being a rope is a yongs gcod.[2]
Alternative translations
Inclusive decision and eliminative decision (Tony Duff)