"Mr Slinkhard doesn't like jinxes, does he? But. 1 think they can be very useful when they're used defensively."
"Oh, you do, do you? ...Well, I'm afraid it is Mr Slinkhard's opinion, and not yours, that matters within this classroom, Miss Granger."
"That is enough ...Miss Granger, 1 am going to take five points from Gryffindor house."
-- Dolores Umbridge and Hermione Granger (OP15)
Defensive Magical Theory was a guide which focused only on the theory of defensive magic, not on the actual practice. Its approach seemed to be that a good defense consists of not fighting back and trying to talk about it instead.
Defence Against the Dark Arts required textbook in Harry's fifth year (OP9). Since Umbridge did little that year in Defence Against the Dark Arts other than set reading assignments from this book, we have an unusual amount of information about its contents. Harryfound it desperately dull. Chapter 1 is entitled "Basics for Beginners" (OP12). Chapter 2 is titled "Common Defensive Theories and their Derivation" (OP15). Chapter 3, which begins on page 34, is titled "The Case for Non-Offensive Responses to Magical Attack" (OP17). In chapter 15, Slinkhard says that counter-jinxes are improperly named, because he believes that "counter-jinx" is just a name given to jinxes to make them sound more acceptable (OP15). Chapter 34 is entitled "Non-Retaliation and Negotiation" (OP29). The book has an index.