Defensive Magical Theory

Defensive Magical Theory is a Hogwarts School of Witchcraft and Wizardry textbook written by Wilbert Slinkhard. Released in, or prior to 1995, it was used by Dolores Umbridge in Defence Against the Dark Arts classes to ensure the students were taught defensive magic in a "secure, risk-free way."

Known contents
"It was desperately dull, quite as bad as listening to Professor Binns. He felt his concentration sliding away from him; he had soon read the same line half a dozen times without taking in more than the first few words."

- Harry struggles through the opening of Defensive Magical Theory

In Chapter 15, the author expresses his opinion that counter-jinxes are not named properly, because he believes that "counter-jinx" is a term simply used to make jinxes seem more acceptable. Apparently, Slinkhard disapproves of the use of jinxes. From this opinion, as well as from the chapter titles and the fact that Dolores Umbridge approves of the book, it can be assumed that Defensive Magical Theory discourages the use of any defensive magic that could be used aggressively. Hermione Granger strongly disagreed and expressed her opinion in one of Professor Umbridge's Defence Against the Dark Arts classes. Although Umbridge was initially impressed that Hermione had read the entire book and was able to quote it, she was quickly irritated when Hermione critiqued the text and coldly deducted points from Gryffindor for "disrupting [her] class with pointless interruptions." It is unknown how Hermione spent her time in Umbridge's classes after this. Possibly she was forced to re-read the book, though given her brainpower, it is likely she spent the time pretending to read while instead engaging her mind in other activities.

The contents of this book are deemed extremely boring by most students, as Harry Potter compared reading it to listening to the History of Magic teacher, Professor Cuthbert Binns, whose droning is enough to put most students to sleep. Harry found himself re-reading the first line half a dozen times, while Ron Weasley was staring at the same spot for a long time.

It is heavily implied that there are enough chapters in the book to keep them reading through the entire year's lessons. Harry almost checks the contents page early in the year, wondering if there could possibly be enough chapters to keep them reading this long, but gets distracted. Much later in the year, the class opens their books to Chapter 34, "Non-Retaliation and Negotiation".

In 1997, Hermione considered this book as she was sorting supplies for their mission to find Voldemort's Horcruxes. She tossed it into the rubbish without a second glance.

Known chapters

 * Chapter One: "Basics for Beginners"(page 5)
 * Chapter Two: "Common Defensive Theories and their Derivation" (page 19)
 * Chapter Three: "The Case for Non-Offensive Responses to Magical Attack" (page 34)
 * Chapter Fifteen: (unnamed) chapter concerning counter-jinxes
 * Chapter Thirty-four: "Non-Retaliation and Negotiation"

Behind the scenes

 * In the film version of Harry Potter and the Order of the Phoenix, the Dark Arts Defence: Basics for Beginners book is used for Umbridge's classes, rather than this book. It has the same level of contents of theories on Defence, rather than practical information on countering the Dark Arts. However, it was constructed and produced by the Ministry of Magic and distributed by Umbridge herself.

Appearances

 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Deathly Hallows