Even if a character is able to cast spells, it does not automatically mean that they are able to learn all spells. Besides racial restrictions, some character professions simply did not spend enough time studying the basics of magic to be able to cast all spells. Those characters are called Half Mages, while the characters who dedicated most of their time to studing the arts of magic are called Full Mages.
In Drakensang, the following professions are Half Mages:
This also applies to the companions of those classes: