Mercury in 9th House synastry is considered very effective for the formation of relationships based on scientific, intellectual, spiritual, and philosophical interests. This synastry is often found in the field of pedagogical and educational activities. Both partners actively stimulate the mental and psychological abilities and aspirations of each other. They are excellent travel companions.
Spending long hours in discussions and intellectual and spiritual conversations, Mercury in Ninth House synastry partners not only do not get tired of each other but become even more imbued with mutual sympathy. At the same time, the “Mercurial” individuality in every possible way contributes to a more practical embodiment of the capabilities of the personality of the Ninth House which, in turn, tries to expand the horizons of the ideological worldview of the “Mercurial” one
In a negative scenario, this synastry is marked by disagreements between partners who blame each other for being self-centered and egoistic.
from F. Sakoyan, L. Ecker
Mercury in 9th House Synastry Explained
Your first acquaintance with a Mercury in 9th House synastry partner can be very effective: the partner will be inspired and tell you something unusual and new. However, Mercury is “imprisoned” in the Ninth House, and the conversations can quickly disappoint you and begin causing unpleasant feelings, not quite, however, of an origin that you understand.
Their true reason lies in the fact that subconsciously you expect a Mercury in Ninth House synastry partner to discover some riddle, an exciting narrative about unknown and mysterious fields of knowledge unknown to you. The partner, of course, is usually clueless about these high expectations. Additionally, your irritation and general displeasure can be caused by their tendency to chat easily about topics that are sacred to you, and in a style that you can only regard as a profanation.
If you articulate your dissatisfaction, your claims will seem to your partner at least unfounded, despite the fact that they may feel a desire to talk about things that are inaccessible to you to expand your horizons.
Working out the Mercury in Ninth House synastry
The partner needs to learn to take discussions of esoteric information seriously while you must understand that the main efforts in the development of areas that are qualitatively new for you, as well as the preparation and implementation of long-distance travel, even if in the company of a partner, mainly falls on your shoulders. Then the two of you can become infatuated with each other, and it is likely that you will carry out a project that each of you alone could not even dream of.
from A. Podvodny