The anonymous text, Upayahrdaya, has not been evaluated correctly in the field of Indian logic. We fixed its historical position between the Hetuvidya of Maitreya and the Nyayasutra of Gautama. The author of the Upayahrdaya was affected by the thought of the Sautrantika school. But his logic consisted of the three sorts of reason; purvavat, sesavat and samanyato drstam. They were used at first by him and enlarged over heretical logic, including Nyaya.
The three sorts of reason might have occurred in the proto-Nyayasutra which was criticized by Nagarjuna and Aryadeva, but the text no longer exists. Anyway, it is sure that they originated in the Carakasamhita, because Caraka related the three sorts of reason, i. e., inference of past thing from present reason, inference of future thing from present reason and inference of present thing from present reason.
The author of the Upayahrdaya shows his affinity to Sautrantika philosophy in such things as provisional cognition of substantial elements, earth, etc. Generally he argues for complete tranquility, non-egoism, non-eternality and so on. Maitreya also composed dialetics and logic from the standpoint of the Sautrantikas in his Yogacarabhumi. But this position is on the way from primary speculation to complete tranquilty, that is, the learning stage (srutamayi bhumih). But our author does not show affinity to Mahayana Buddhism.
This text was translated into Chinese 472 A. D. as Fangbianxin lun 方便心論 (Taishô no. 1632), and the Sanskrit original as well as Tibetan version are not extant. But its abundant dialectics fascinate us, researchers of Indian logic.