From the introduction:
The magic system of the Harry Potter (HP) world gets a bad rap. Within fantasy and sci-fi circles, it is often considered a particularly weak example of worldbuilding: vague, unexplained, and at times prone to inconsistencies driven by the plot. I believe this to be an unfair characterisation. This is for two reasons.
Firstly, I believe we know a lot more about the HP magic system than most casual readers think. The absence of one character explaining magic comprehensively to another does not mean that the magic system is unexplained. It is in fact a common maxim of good writing to show rather than tell: readers buy into ideas more when they see them in action rather than when they are told about them. And in the HP books we see a lot of magic, hear characters discussing magic, and witness the results of magic on the social structure of the wizarding world. All these scenes give clues that the attentive reader can piece together to gain insight of surprising depth into the HP magic system.
Secondly, I think JK Rowling does a very different kind of worldbuilding to an author like Brandon Sanderson, who is famous for his “First Law of Magic”:
An author’s ability to solve conflict with magic is DIRECTLY PROPORTIONAL to how well the reader understands said magic.