Considering "the heart of one single mind embracing ignorance and dharma-nature simultaneously", which is the core concept of the Perfection Doctrine of Tiantai School, this paper discusses that "ignorance" is a concept of epistemology and axiology while "dharma nature" is a concept of ontology. In this paper, the author tries to explain the exact meaning of Master Zhi-Yi's theories based on "the heart of one single mind embracing ignorance and dharma-nature simultaneously", namely "ignorance is dharma nature while dharma nature is ignorance", "all dharmas are mind while mind is all dharmas", and "three thousand worlds exist where mind exists". Based on the explanation, this paper responses to the academic community's inquiry about whether Master Zhi-Yi's theories fall into dualism or monism. This paper presents the following main ideas: Reviewed from the perspective of dynamic intellectual practice, the differentiation between "ignorance" and "dharma nature" reveals the dualistic structure of "the heart of one single mind". Regarding "ignorance" and "dharma nature", there is no need to question about "which onegenerates the other" or "whether they exist simultaneously or asynchronously". In nature, ”the heart of one single mind embracing ignorance and dharma-nature simultaneously” is neither a cosmological concept nor an ontological concept. It reveals that extrication-oriented value practice is a sort of intellectual activity, in which a thing's meaning cannot be found without recognition of its being. Hence, the theory of "one mind containing three thousand worlds" based on this teaching is in deed a false dualistic conclusion, even though it presents a dualism (origination) meaning to a certain extent.