Sensation and dependent origination
There are several different detailed or expanded formulas for dependent origination in the Buddhist canonical literature. The Mahāpadāna Suttanta of the Dīghanikāya, for example, enumerates ten factors (nidāna). Mahāvaggo 1.1 of the Vinayapiṭaka, and numerous texts in the Suttapiṭaka, enumerate twelve factors. Still other canonical texts enumerate nine, six or even fewer. But for philosophical purposes the more important version of dependent origination is the shorter one that states the basic principle of causation in these words:
This [effect] comes into being when that [cause] is present. This arises owing to the arising of that. This does not arise when that is absent. This ceases owing to the cessation of that.
The philosophical importance of this formula of dependent origination resides in part in the fact that it is plainly reflected in the definitions of evidence (hetu) offered by Dignāga and Dharmakīrti. In his Pramāṇasamuccaya 2.5cd, Dignāga defines an inferential sign as a property that is “present in the inferable object and what is similar to it and absent in their absence.” Similarly, Dharmakīrti says in the Nyāyabindu “an inferential sign has three characteristics: it must be known to be present with what is to be inferred, present only with what is like the subject and entirely absent in what is unlike the subject.”
According to Dharmakīrti, one thing X can serve as a sign of a second thing Y only if there is a natural relation between X and Y. Speaking from a metaphysical point of view, Dharmakīrti says that there are only two situations in which this kind of natural relation is found: 1) when Y is a cause of X, and 2) when X and Y have exactly the same set of causes. The stock example of the first situation is that smoke can serve as a sign of fire only because fire is a cause of smoke, which means that smoke is present when fire is present and absent when fire is absent. The stock example of the second situation is that the fact that something is an oak can serve as a sign that it is a tree, because the set of causes that make the property of being an oak arise are exactly the set of causes that make the property of being a tree arise; in other words, it takes no more and no less to make a given particular thing a tree than it takes to make it an oak.
It is not difficult to see that the principle of causality stands behind Dharmakīrti’s theory of inference to the same extent that it stands behind the Buddha’s notion of how one attains freedom from distress. And so if the Buddha could say that to see dependent origination is tantamount to seeing the Buddha himself, Dharmakīrti would be entitled to say that to know the theory of inference is also tantamount to knowing the Buddha.
Now the question can be asked: what kind of knowledge is involved in seeing dependent origination? Is it sensation or inference? Given that the subject matter of a sensation can be only that which exists in the immediate present and that this type of cognition is said to be completely free of any admixture of recollections of the past or anticipations of the future, the knowledge described in the short formula of dependent origination cannot be sensation. For in order to know that X is present when Y is present and absent when Y is absent requires at least two moments, one of shared presence and a second of shared absence. Furthermore, one must retain the knowledge of one of these moments during the second moment, so that the second moment must involve some degree of thought on top of what is being immediately sensed. The cognition of even one instance of dependent origination, being the apprehension of a temporal process, is similar to the discernment of a melody, which can never be grasped if one is aware only of the note that is being played in the present instant.
The full grasp of dependent origination is, however, much more than the apprehension of a single temporal process. It is really a generalization that is supposed to be true of all sentient beings at all times. This becomes more clear when one looks at the slightly expanded formulas in which it is typically said that any form of desire (tṛṣṇā) ultimately results in some form of disappointment or distress (duḥkha). It would hardly rank as a momentous discovery if all the Buddha had meant to say was that one particular episode of desire in his life resulted in one particular episode of frustration. The Buddha’s first sermon is not portrayed as his own personal recollection of, for example, scowling when he was not given permission to fulfill his desire to ride a white pony on the day of the fourth anniversary of his birth. Rather, it is portrayed as his proclamation of a discovery that all desire anywhere eventually results in some degree of frustration of some kind. It is, in other words, a piece of knowledge that has all the characteristics that Dharmakīrti attributes to inference.