Complementarity
Complementarity is a corollary of duality as applied to elements, functions, and dichotomies, all of which describe how and why duals are the most compatible types.
Complementary IM elements
Quadra values comprise two pairs of complementary elements, which must be either both valued or both subdued.
Ne and Si
Ni and Se
Fe and Ti
Fi and Te
Complementary functions
Function x
in a type's Model A always contains the same element as function x +/- 4
in its dual's Model A. Thus the complementation of elements may be generalized to complementation of functions.
Leading function and Suggestive function
Creative function and Mobilizing function
Role function and Ignoring function
Vulnerable function and Demonstrative function
Complementary dichotomies
For any given dichotomy, one's dual has to have either the same or the opposite trait. Quadra values become a specific instance of this, due to the dichotomies of merriness and seriousness (Fe/Ti vs. Fi/Te) and judiciousness and decisiveness (Si/Ne vs. Se/Ni).