Mercade
the Counsellor
There are 10 trees. You have to unlock the trees one at a time, but once open they are open. As stated by Stealth NSK, some are mutually exclusive in that you cannot unlock e.g. rationalism if you've already opened piety in the past. But once you've opened piety it stays open during the remainder of the game. If you then open freedom, then you'll have piety and freedom open at the same time.Happiness required for a golden age! that makes sense - and I'm happy (no pun intended) to learn of it!
Remind me, you can only adopt ONE policy at a time? Or you can have multiple, but some are mutually exclusive?