In Molina's system, 4s are 4EI and 8s are 8IE.
That means 4s are from the Extrinsic center, and are the Intrinsic manifestation of that center.
Conversely, 8s are from the Instrinsic center, and are the Extrinsic manifestation within that center.
So yes, the two types are very much, in a sense, opposite sides of the same coin.
I think this explains the oft-mentioned chemistry between the two.
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Other similar pairings:
1s and 5s
2s and 7s
I don't know if similar such chemistry exists between those pairings.
I have heard of 1s and 5s getting along, I think, but not 2s and 7s.
I also guess there's a distinguishing factor for 4s and 8s here, in that they're the only ones who have both the Intrinsic and Extrinsic value dimensions within their makeup -- 1IS and 5SI, and 2ES and 7SE, all have the Systemic paired with either the Intrinsic or Extrinsic -- and I could see the complete opposition of value realms (i.e., Intrinsic vs Extrinsic) creating a more polarized, volatile, combustible dynamic/energy/tension between 4s and 8s than any other pairing.
Which makes sense right?
Cuz when I imagine 8s and 4s, I do imagine, essentially, the stuff of romance novels: sparks, chemistry, insane passion.
And I imagine it more with that pairing than with any other.
(Which, once again, in terms of what I've written on here about sexual polarity [basically just explaining David Deida's {and, by extension, much mythological/religious/spiritual teaching throughout history} teachings], would make sense.)
Sexual chemistry is fueled by masculine-feminine polarity, and, well, 8s are probably the most masculine type, and 4s the most feminine type.