This article deals with the sahopalambhaniyama （SUN） argument, Dharmakīrti’s argument for the theory that cognition possesses mental images in itself （sākāravijñānavāda）, focusing on an instance in the argument: “like two moons.” The argument is that “because they are invariably apprehended together （SUN）, blue and the cognition of it are not different, although they appear as being different,” to which I introduce two different levels of viewpoint: the true and the false. Not being different is the true, and being different is the false; the SUN is situated between the two. Therefore, it should be considered to which level the SUN belongs, as it influences the meaning of the two moons. Normally, the two moons are false objects caused by an eye disease, and their cognition is false. However, it is not only false if used as an instance of the SUN. I examine the argument in Dharmakīrti’s Pramāṇaviniścaya and Pramāṇavārttika using the interpretations of Devendrabuddhi, Śākyabuddhi, Dharmottara, and Prajñākaragupta. Emphasis is put on Prajñākaragupta’s interpretation in relation to his fundamental idea that cognition is various but unified （citrādvaita）. I conclude by pointing out that Śākyabuddhi, Dharmottara, and Prajñākaragupta shared a common interest in the identity of the cognition of two moons but had different opinions on whether the cognition is true or false.
