Hello dear Rinpoche! I have to ask if I give the right answers to my son (21 years old) . He asked me if Buddhanature and true nature of mind is the same. I´d at first say, yes. For the practice of a Vajrayana practitioner it is the same.
From philosophical point of view it is not totally the same. It depends on personal opinions, not everybody sees it as the same. That depends on which tenet system the practitioner follows. A hinnayana practitioner will say it is not the same, and might even say that buddhanature is a wrong concept. If he believes only in Hinnayana, like Theravadins do. I think, the true nature of mind is same as suchness in Hinnayana/Theravada?
And we as Mahayana practitioners who believe it is the same from the aspect of practice, also differentiate from a philosophical point of view. Most of the explanations on emptiness that the Buddha Shakyamuni gave are very different from what he taught in the Tatagathagarba-Sutra. The tatagathagarba-sutra is only kind of seed of the Buddhanature philosophy. Buddhanature was taught elaborately by Mahayana Masters who lived after the Buddha Shakyamuni.
But the proof that both is the same, that it is not a contradiction, is not easy to do.
I hope it is possible that you correct my thoughts. Maybe I am totally wrong.....I hope this is not just a word-salad here, understandable to nobody....