Turbulent Spirit

Hume says that the order of the dukes is often subject to a "turbulent spirit" when there is a weak king.

Turbulent means disorderly. I think Hume's first priority is a political order in which people can live their lives in peace, without being harmed by others or by government. Tumult and turbulence are a threat to that order. A weak reign in itself is probably a threat to this good order, because a weak king will not be able to execute the laws and promote justice. But the turbulence of the dukes is an additional threat.

In the history of Richard, a weak king, the turbulent spirit of the Duke of Glocester and then later that of Hereford will lead to Richard's downfall.