Continuing from this post, for those not inclined to read Thakchoe’s lengthy and very nuanced book, see his shorter Stanford Encyclopedia of Philosophy entry on the same topic. It too is quite nuanced on the subtle differences between the four main Tibetan Buddhist schools. The following is from the concluding implications section sort of summing up:
“Gelug considers the two natures of each phenomenon as the defining factor of the two truths. It argues that the conventional nature of an entity, as verified by a conventionally reliable cognitive process, determines the defining criterion of conventional truth; the ultimate nature of the same entity, as verified by an ultimately reliable cognitive practice, determines the defining criterion of ultimate truth. Since both truths are ontologically as well as epistemologically interdependent, knowledge of conventionally real entitity as dependently arisen suffices for knowledge of both truths. In contasty non-Gelug schools—Nyingma, Kagyü and Sakya Non-Gelug, as we have seen, rejects Gelug’s dual-nature theory, treating each conventional entity as satisfying only the definition of conventional truth and taking the definition of ultimate truth to be ontologically and epistemologically transcendent from conventional truth. They argue, instead, it is through the perspectives of either an ordinary being or an unenlightened exalted being (āryas) that the definition of conventional truth is verified—fully enlightened being (buddhas) do not experience the conventional truth in any respect. Similarly, for non-Gelug, no ordinary being can experience the ultimate truth. Ultimate truth transcends conventional truth, and the knowledge of empirically given phenomena as dependently arisen could not satisfy the criterion of knowing ultimate truth.
“For Gelug, there is an essential compatibility between between the two truths, for the reason that there is a necessary harmony between dependently arisen and emptiness of intrinsic reality. As dependently arisen, empty phenomena are not constructions of ignorant consciousness, so neither is conventional truth such a construction. Both truths are actual truths that stand on an equal footing. Moreover, according to this view, whosoever knows conventional truth, either directly or inferentially, also knows ultimate truth; whosoever knows ultimate truth, also knows phenomena as dependently arisen, and hence knows them as empty of intrinsic reality. Where there is no knowledge of conventional truth, the converse applies. For non-Gelug, the incommensurability between dependently arisen and emptiness of intrinsic reality also applies to the two truths. Accordingly, whosoever knows conventional truth does not know ultimate truth, and one who knows ultimate truth does not know conventional truth; whosoever knows phenomena as dependently arisen does not know them as empty, whereas whosoever knows phenomena as empty does not know them as dependently arisen.
“While Gelug thus distances itself from the subjective division of the two truths, Nyingma, Kagyü and Sakya attempt to demonstrate the validity of their view by arguing that perspective provides the primary basis for the division of the two truths. Unlike Gelug, non-Gelug schools hold that the two truths do not have any objective basis. Instead they are entirely reducible to the experiences of the deluded minds of ordinary beings and the experiences of the wisdom of exalted being.
“According to Gelug, the agent who cognizes the two truths may be one and the same individual. Each agent may have all the requisite cognitive resources that are potentially capable of knowing both truths. Ordinary beings have only conceptual access to ultimate truth, while exalted beings, who are in the process of learning, have direct, but intermittent, access. Awakenened beings, however, invariably have simultaneous access to both truths. The view held by non-Gelug argues for separate cognitive agents corresponding to each of the two truths. Ordinary beings have direct knowledge of conventional truth, but are utterly incapable of knowing ultimate truth. The exalted beings in training directly know ultimate while they are meditative equipoise and conventional truth in post meditative states. Fully awakened buddhas, on the other hand, only have access to ultimate truth. Awakened beings have no access to conventional truth whatsoever from the enlightened perspective, although they may access conventional truth from unenlightened ordinary perspectives.”