Abstract: FENG Qi's ontology of "four domains", including the domain of things as such, that of facts, that of possibilities and that of values, embodies the unity of ontology, epistemology and axiology. However, when things as such, facts, possibilities and values are put into different ontological "domains", it leads to a logical danger that they would be separated from each other. In contrast, the interaction between the world of things as such and the world of reality in the "two worlds" presents another metaphysical horizon. In these "two worlds", the ontological difference by no means excludes the comprehensiveness of the world of reality and the relevance of different ontological "domains". While philosophers in the history such as Russell, JIN Yue-lin and Habermas mainly understand facts from the perspective of epistemology, FENG Qi emphasizes the ontological dimension as well as the epistemological dimension of "facts". This is based on the correlation between interpreting the world and changing the world. From the perspective of metaphysics, this correlation is the premise of transforming the world of things as such to the world of reality. In this regard, FENG's notion of facts implies the "two worlds", which also overcomes the possible separation in the "four domains" to some extent.

Key words: possible separation in the “four domains”, relevance of the “two worlds”, fact