Astus wrote:I might be mistaken here but it wasn't Nagarjuna who mentioned that element but Tsongkhapa. Also, it seems quite unnecessary to explain the efficacy of karma. Third, it is not explained in the text itself nor does it sound really convincing how such an element exists.
It is indeed Nāgārajuna's position, the name of the dharma in question is avipraṇāśa. MMK 17:13-20 explicates this doctrine. Candrakriti clarifies. This is not an invention of Tsongkhapa's. Nāgārjuna affirms in verse 17:20 "The avipraṇāśa of karma is the teaching of the Buddha."
This is the sole place in the MMK where Nāgārjuna actually advances a shravaka position he likes. See Mabja, ppg. 353-359.
As I said, this is originally a Sammitya doctrine. See also Karmasiddhiprakarana, ppg, 87-91 for a translation of Candrakirti's take.
Nevertheless, even though among various shravaka theories that Nagarjuna examines, this is one he apparently likes, still, from a Madhyamaka perspective he finds the idea of this avipraṇāśa unnecessary even though it is a teaching of the Buddha.