Claim. Every entity has two pairs of dual characteristics — yang/yin and internal nature/external form — but internal nature and external form (sungsang/hyungsang) are more fundamental than yang/yin, with internal nature standing as subject partner to external form as object partner.
Elaboration. Per 1.1. The Dual Characteristics of God: “there is another pair of dual characteristics in reciprocal relationship which are even more fundamental to existence than the dual characteristics of yang and yin. Every entity possesses both an outer form and an inner quality. The visible outer form resembles the invisible inner quality.”
The relationship: “The internal nature is intangible and causal, and stands in the position of a subject partner to the external form; the external form is tangible, resultant, and stands in the position of an object partner to the internal nature. The mutual relationships between these two aspects of an entity include: internal and external, cause and result, subject partner and object partner, vertical and horizontal” (ibid).
Paradigm example: a human being’s mind (sungsang) and body (hyungsang). The body “is a visible reflection of the invisible mind”; the body moves “according to its commands in such a way as to sustain life and pursue the mind’s purposes” (ibid). All beings — animals, plants, atoms, even subatomic particles — have something corresponding to the human mind directing their external form toward a purpose.
This is load-bearing for all subsequent DP doctrine: God’s own structure, the four position foundation, the cosmos of incorporeal/corporeal worlds, and the spirit-world/physical-world relationship all derive from this single fundamental.