Muggles' Guide to Harry Potter/Magic/Charms

Overview
Charms is a course that teaches how to cast the class of spells known as Charms. These are spells that alter an object without changing its essential nature. Given a teapot, the spell that makes it tapdance across the desk would be a charm, the spell that turns it into a tortoise would not. This is a core subject, required of all Hogwarts students until at least their fifth year. While the course is offered to sixth and seventh year students, admission is limited to those who have shown better than average abilities in Charms based on their O.W.L. grades.

The Trio take Charms from their first to their sixth years at Hogwarts.

Extended Description
The Charms class is taught by Professor Flitwick. Spells taught in this class include Wingardium Leviosa, Summoning and Banishing, Aguamenti, and turning vinegar into wine. Because it is a lab class, with much wand work and people saying spells, it is often a nearly ideal place for Harry, Ron, and Hermione to have more or less private conversations.

A number of significant events happen in and around Charms class. The first spell that any of the Trio learn properly, and apparently the first one actually cast in their school career, is the Wingardium Leviosa charm cast by Hermione. Her apparent self-satisfaction at being the first in the class to master this charm causes Ron to comment to Harry about that being the reason she has no friends. Hermione overhears this, and bolts to the girls' washroom to cry. Ron and Harry rescuing Hermione from the mountain troll that evening results in the creation of the Trio.

Charms class, as mentioned, is a lab class for much of the series, and as such provides many opportunities for conversation among the Trio, plus a certain amount of slapstick humour (Ron's vinegar explodes when he tries to turn it into wine, for instance, in the sixth book). The main purpose of Hogwarts, of course, is lessons, though as the main conflict of the story is extracurricular much of the action will take place outside the classrooms. The reader may come to anticipate those sections of the book that occur in class, partly for the insight into the difficulty of learning magic, and partly for the associated humour.

It appears that some witches, notably Mrs. Longbottom, Neville's grandmother, consider Charms to be a "soft option", an easy course even at N.E.W.T. level. Against this, of course, we have to weigh the difficulty Harry seems to have with the Summoning charm, and the fact that Professor Flitwick wants to discuss Harry's near-perfect use of that charm in the First Task of the Triwizard Tournament in Harry's fourth year. Clearly this charm is much more involved than simply pointing your wand and saying "Accio!" Additionally, we find that the redoubtable Mrs. Longbottom apparently did quite poorly on her Charms O.W.L., and we can imagine there to be a certain bias in her views.

Analysis
The definition of Charms, according to the author, is "those spells which do not change the intrinsic character of the object on which the spell is cast". As mentioned in the Overview, the spell which causes the teapot to tapdance across the desk is a Charm because it is still a teapot, albeit one with legs, feet (with the equivalent of tap shoes), and the propensity to emulate Fred Astaire. This can be expanded easily to include spells such as Aguamenti, which causes the caster's wand to send out a stream of water, and Lumos, which causes the wand to emit light. In both these cases, the object modified is the caster's wand, which remains a wand, just one that also behaves like a garden hose or a flashlight. The definitions are, however, somewhat loose; in Transfiguration class, we see that Ron and Harry are having troubles with a silencing spell, and the reader may note that a silenced toad or a silenced raven remains a toad or a raven.