In the second half of the 14th century, however, certain royal taxes, levied throughout the Crown's domain, tended to become permanent and independent of the vote of the estates. This result drew from many causes, particularly, the Crown endeavoured to transform and change the nature of the "feudal aid" to levy a general tax by right, on its own authority, in such cases as those in which a lord could demand feudal aid from his vassals. For instance, the Crown thus raised the necessary taxes for twenty years to pay the ransom of King John II of France without a vote of the Estates General, although the assembly met several times during this period. Custom confined this tendency. During the second half of the 15th century, the chief taxes, the "taille", "aids" and "gabelle" became definitely permanent for the benefit of the Crown. In some cases there was formal consent of the Estates General, as in 1437 in the case of the "aids".