Four principles of reasoning

Four principles of reasoning (Wyl. rigs pa bzhi)

1. the principle of causal efficiency (bya byed kyi rigs pa)
   All functions of a certain cause producing a certain effect are called the reasoning of function.
2. the principle of dependency (ltos pa’i rigs pa)
   The fact that everything that is an effect, such as the sprout, is definitely dependent upon its own causes is called reasoning of dependence.
3. the principle of nature (chos nyid kyi rigs pa)
   Since the efficient function of a thing and its dependence on causes are the very character of that thing, these two principles of reasoning related to them are themselves contained within the wider principle of the nature or evidence of things. [...] When one reaches this point, no other valid proofs are necessary―just as there is no need to explain the reason for a fire's heat. Conventional and ultimate reasonings are both referred to as reasoning based on the [nature or] evidence of things. The relative nature or mode of being of fire is that is throws out heat; the ultimate nature or mode of being of fire is that it lakes inherent existence. Thus a thing's mode of being is established without mistake by both valid cognitions (conventional and ultimate) together, and not by only one of them in isolation.
4. the principle of establishing a proof (‘thad sgrub kyi rigs pa)
   How is this proof being established? It is established by means of the two types of validity: the validity of direct perception which is to perceive these two things: the conventional meaning of whatever appears and the ultimate meaning of how it is, and the validity of inference which is to infer unmistakenly something other from the perception of a sign that has the capacity for estimating something that is hidden.