• Aggressively conventional-minded: they believe not only that rules must be obeyed, but that those who disobey them must be punished.
• Passively conventional-minded: they're careful to obey the rules, but when other kids break them, their impulse is to worry that those kids will be punished.
• Passively independent-minded: they don't care much about rules and probably aren't 100% sure what the rules even are.
• Aggressively independent-minded: when they see a rule, their first impulse is to question it. Merely being told what to do makes them inclined to do the opposite.

The four types are not equally common. There are more passive people than aggressive ones, and far more conventional-minded people than independent-minded ones. So the passively conventional-minded are the largest group, and the aggressively independent-minded the smallest.

Why do the independent-minded need to be protected, though?

Because they have all the new ideas. To be a successful scientist, for example, it's not enough just to be right. You have to be right when everyone else is wrong. Conventional-minded people can't do that.

In the past, the way the independent-minded protected themselves was to congregate in a handful of places — first in courts, and later in universities — where they could to some extent make their own rules.

For the last couple centuries at least, when the aggressively conventional-minded were on the rampage for whatever reason, universities were the safest places to be.