Is there one instinctual stacking match that is superior to all the other ones, and could classify as your "soulmate" or most compatible match? Or in other words, is there something like an "Instinctual Dual"?
I have expanded upon the romantic compatibilities of the instinctual stackings before, but in that article I was not looking at the stackings from a Socionics angle, mostly.
However, there do appear to be similar dynamics concerning the instinctual stacking combinations and certain Intertype relations in Socionics.
There are two key principles from Socionics intertype relations which can be applied to the Enneagram instinctual matches: The principle of being very similar (or not) in strengths and weaknesses, and the principle of valuing the same things in life (or not).
In that manner, I do have observed and experienced dynamics between the stackings that are reminiscent of certain intertype relations. This article has described those dynamics to some extent already, however I find it is incomplete and could benefit from more input, which I provide in the following.
Same stacking: Identity
e.g Sp/Sx with Sp/Sx
These stackings are identical to each other. They value the same things in life. However, they also cannot help each other when it comes to their weaknesses. In that manner, they are like Socionics Identicals.
Same blindspot, opposite flow: Semi-Duality
e.g Sp/Sx with Sx/Sp
These stackings share similar values; they both have the same blindspot, but also are in opposite flows. They both can help the other at what they value the most, however being in opposite flows creates a certain dissonance – the other person's help or input is not always exactly appropriate. Also, they both share the same blindspot, a certain weakness, that neither can help the other at. In that manner, they are like Socionics Semi-Duals.
Same flow, different blindspot: Benefit
e.g Sp/Sx is the Benefactor of Sx/So; Sp/Sx is the Beneficiary of So/Sp
These stackings partially share the same values, sharing one instinct and the same flow. One stacking is proficient at what the other stacking is lacking in and valuing the most; however, the reverse doesn't apply. The other stacking is just as if not weaker and more negligent at what the former stacking is valuing and would benefit from some aid in. In that manner, they are like Socionics Benefactor and Beneficiary.
Same first instinct, opposite flow: Kindred
e.g Sp/Sx with Sp/So
These stackings can relate to each other on the basis of their shared first instinct. However, the second instinct of the other as well as their opposite flow can be disorienting or at worst irritating. In that manner, they are like Socionics Kindred partners.
Same second instinct, opposite flow: Quasi-Identity
e.g Sp/Sx with So/Sx
These stackings share similar weaknesses and strengths. However, being in opposite flows and blind to what the other values the most they hardly or not at all share the same values. In that manner, they are like Socionics Quasi-Identicals.
So to answer the question: No, there is actually no "Instinctual Dual".
There is not one ideal instinctual stacking for you. However, certain ones are surely a better fit than others, both romantically and platonically. And these dynamics do have an impact on "real" Intertype dynamics. For instance, opposite Quadra interactions can to an extent be more enjoyable when the individuals have an Identical stacking combination. Or favourable ITRs can be worsened by a Quasi-Identity stacking combination.
I tend to recommend everyone to stay away from Quasi-Identity stacking individuals when it comes to romantic relationships. Based on my observations, only Duality and Identity couples have made it work long-term (=marriage).
A similar principle seems to apply to Kindred stacking combinations; they are best paired up with individuals of the same "real" Quadra.
Bottom-line for dating: Do not date a Quasi-Identity stacking when you are looking for a happy long-term relationship (esp. marriage), unless you are Duals or Identicals. Be careful about dating an individual who has the Kindred stacking and is neither your "real" Dual nor Identical; a relationship like that is unlikely going to last. The other three stackings are more or less good to go for, depending on your personal preferences.
Friendship-wise, an Identical stacking person is probably the easiest and most enjoyable to get along with. All the other stackings are more or less good to go for, apart from the Quasi-Identity one; being of the same Quadra is likely essential for it to work fine.
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