In Stellaris government ethos works on four scales:
- 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!