Symmetric relations.
Signs of the corresponding functions are different.
Function interactions: 1 ↔ 5, 2 ↔ 6, 3 ↔ 7, 4 ↔ 8.

The partners complement each other by dimensions and track (mental or vital) of corresponding functions. Information from the ego block interacts with the respective functions of the partner's superid  (1 ↔ 5, 2 ↔ 6). Information from the function 1 has suggestive effect and information from the function 2 activates the partner. Receiption of the information  by the superid block is accompanied by positive control emotions and "switches on" the functionning of the partner's entire model. Thus, every output of information from the ego block every time activates the partner's superid, switching on his ego block which in return activates the superid of the first partner.

Interaction of the superego and id blocks (3 ↔ 7, 4 ↔ 8) does not result painful for respective superego of each of the partner because of self-centered attitude of id blocks . (for more detailed description see «Дуальные отношения ЭИИ — ЛСЭ»).

The difference in the signs of corresponding functions causes lack of information, which makes neccessary to look for such information  in the socion. This provides condition for the system's openness. Both partners are either rational or irrational which favors better understanding.

The duality relations are most comfortable for marriage.