Thanks cmdr, how is it possible to determine the ethos, is it via in game info or external tools?
It used to be in the faction local news articles - at the end they thank their membership, and the wording is ethos-specific. I haven't actually checked one since 3.5.2 to make sure it's still there, though... If it is, that's the easy way.
Otherwise, you can deduce most of it fairly easily from obvious signs in-game (it's not in the journals or similar):
1) If it offers lots of smuggling missions it's Criminal
2) If it doesn't do that, but has black markets at stations it owns, it's Social
3) If it doesn't (generally) have black markets, it's either Corporate or Authoritarian. I've seen some indication that Corporates disable black markets while Authoritarians remove them entirely, but that's hard to reliably test.
Social, Corporate and Authoritarian factions have Elections if the other faction is the same ethos, and Wars/Civil Wars if it's a different ethos. Criminal factions always fight Wars/Civil Wars even with each other. This can be used to determine Corporate or Authoritarian for an unknown faction, if you have one you do know, especially if you have a good history of previous conflicts.
For factions in the bubble, the following will be accurate 99%+ of the time:
Social: Communist, Cooperative, Confederacy, Democracy
Corporate: Corporations
Authoritarian: Dictatorship, Feudal, Patronage, Prison Colony
Criminal: Anarchy
Theocracies in the bubble are either Social or Authoritarian - as far as I can tell, the older Theocracies (most NPC) are Social and the newer ones (most PMF) are Authoritarian.
This can't be relied on for non-bubble factions hand-edited in by Frontier - Colonia is very different, and Explorers' Anchorage has five democracies (3 Social, 2 Corporate) at it, for example.