If you have two Citizens next to each other on your board and you want to increase one of them, can you take the Philosopher action to move one up, causing the other one to go down? Or is discarding a cube from your Oracle the only way to do this?
Well, it is right where education is explained on page 7 bottom left:
Two groups of people are in the same row of the population chart. The wooden cubes in the same row may not be on the same space and may also not “move past each other”. If the wooden cubes in a row are on adjacent spaces and the player receives another person of one of the two groups, he needs to reset the other wooden cube. A player may not have more than 6 people in a group; awooden cube, may never be moved further than the “0” space.
If two cubes are touching and you move forward one of these one space, the other is pushed backwards only one space, NOT to zero. Thus, the total of citizens in this row remains 6, but the mix is changed.