How does government ethos change work in Stellaris?

Question

In Stellaris government ethos works on four scales:

• Pacifist-Militarist
• Authoritarian - Egalitarian
• Xenophobe - Xenophile
• Materialist - Spiritualist

At any stage empire can have only three ethics or one fanatical and one regular (i.e. you can be Pacifist-Egalitarian-Spiritualist* or Militarist-fanatical Xenophile**)

But you can change the ethos in game, either by rare and special events ("Shrines of the Old Gods" for example can make you more spiritual) or by embracing a faction within your empire (embracing pacifists would make you go towards "fanatical pacifist" for example)

But how is it determined which of the ethics you would loose? If I am xenophobe-pacifist-materialist and now want to go somewhere in the egalitarian-authoritarian scale, which ethic will I lose? Is it a random one or is there a specific rule?

^{*AKA "Space Hippies"}

^{** They will love you, whether you want it or not! And they will make you love them!}

Answer 1

You lose the ethos with the least population support. Or the opposing one if you have, for example, pacifist and are going to embrace militarist.

Here is a dev diary about it: https://forum.paradoxplaza.com/forum/index.php?threads/stellaris-dev-diary-61-indoctrination-unrest-and-faction-interactions.999954/

In particular: "Which ethic is lost or added is determined by attraction, so if you are Spiritualist, Xenophobe and Authoritarian and make a shift towards Militarist, whichever of Spiritualist, Xenophobe and Authoritarian has the lowest attraction in your empire will be lost as a Governing Ethic."