The effective powers of the Estates General likewise varied over time. In the 14th century they were considerable. The king could not, in theory, levy general taxation. Even in the provinces attached to the domain of the Crown, he could levy it only where he had retained the "haute justice" over the inhabitants, but not on the subjects of lords having the "haute justice". The privileged towns generally had the right of taxing themselves. To collect general taxes, the king required consent of the lay and ecclesiastical lords, and of the towns. This amounted to needing authorization from the Estates General, which granted these subsidies only temporarily and for fairly short periods. As a result, they were summoned frequently and their power over the Crown became considerable.