Ancient books about politics spent as much time talking about friendship as about justice.  Books written for the training of young rulers, called “mirrors for princes,” used to warn that tyrants have no friends, only sycophants.

I think many of my students consider such warnings odd.  What are they doing there?

The warning is a check against tyranny, but one which is rooted in moral psychology rather than in constitutional procedures.  What drives it is the reflection that rulers are tempted to tyranny, and must be provided with motives not to give in.

You would never find such a warning in a civics textbook today.  Why is that?

Is it because we are so convinced that purely procedural checks against tyranny will be sufficient?  Because we are so contemptuous of the suggestion that even rulers might wish to have friends?  Or because we are so naïve as to think no one would ever wish to be a tyrant?