The Identity and Difference of the Two Truths (Garfield)

One of the Buddha's deepest insights was that there are two truths, and that they are very different from one another. They are the objects of different kinds of cognition, and they reflect different aspects of reality. They are apprehended at different stages of practice. Despite the importance of the apprehension of ultimate truth, one can't skip the conventional. Despite the soteriological efficacy of ultimate truth, even after Buddhahood, omniscience and compassion require the apprehension of the conventional.

Nagarjuna's deepest insight was that despite the vast difference between the two truths in one sense, they are in an equally important sense identical. We can now make better sense of that identity, and of why the fact of their identity is the same fact as that of their difference. The ultimate truth is, as we know, emptiness. Emptiness is the emptiness not of existence but of inherent existence. To be empty of inherent existence is to exist only conventionally, only as the object of conventional truth. The ultimate truth about any phenomenon, according to the analysis I have defended [in this essay], is hence that it is merely [even so] a conventional truth. Ontologically, therefore, the two truths are absolutely identical. This is the content of the idea that the two truths have a single basis, which is empty phenomena. Their emptiness is their conventional reality; their conventional reality is their emptiness.

But to know phenomena conventionally is not to know them ultimately. As objects of knowledge (that is, as intentional contents of thought, as opposed to as mere phenomena; that is, as external objects considered independently of their mode of apprehension) they are objects of different kinds of knowledge, despite the identity at a deeper level of these objects. Thus the difference. But the respect in which they are different and that in which they are identical are, despite their difference, also identical. A mirage is deceptive because it is a refraction pattern, and it is the nature of a refraction pattern to be visually deceptive. The conventional truth is merely deceptive and conventional because, upon ultimate analysis, it fails to exist as it appears - that is, because it is ultimately empty. It is the nature of the conventional to deceive. Ultimately, since all phenomena, even ultimate truth, exist only conventionally, conventional truth is all the truth there is, and that is an ultimate, and therefore a conventional, truth. To fail to take conventional truth seriously as truth is therefore not only to deprecate the conventional in favor of the ultimate, but to deprecate truth per se. In that way lies suffering. (from "Taking Conventional Truth Seriously: Authority Regarding Deceptive Reality", by Jay L. Garfield, in Philosophy East and West, July 2010)