This is one of those slightly messy areas of canon - which always gives writers a fair amount of latitude. So how do you prefer to depict counter-spells? Let's have a look at how they're used in canon: So, to summarise, I think that it's clear what system JKR intended to implement: 1. Counter-spells either undo something that occurring, or prevent/block it from happening in the first place. 2. Generally, counter-spells are used to undo other magic, but they can also be used directly to stop a specific thing from happening in the first place, like hiccups. 3. Specific spells have specific counters - such as Libracorpus for Levicorpus, or the counter-jinx for Jelly Legs. 4. Hogwarts students not only learn counters by rote, but also how to develop counters themsleves (Harry's OotP Charms homework). 5. While the Shield Charm can block "minor" dark magic, more powerful magic would require you to know the specific counter-curse to block. 6. Like most spells, Counters can be cast to take effect immediately OR be cast in an object or place to take effect perpetually. However, there are a number of complications to this view: - In the event, JKR ended up increasingly leaning on the Shield Charm, to the point that it became a universal defence from every possible harm, magical, mental or physical - with the sole exception of the Killing Curse. We're told twice, once in GoF and once in OotP, that the Shield Charm is for minor jinxes only. But then we see the Shield Charm used to block powerful spells from Bellatrix, Dolohov, and Snape; we also see it deployed by Bellatrix, Lupin and Tonks in serious fights. We see Harry use it to cut Voldemort off from the rest of the Great Hall in DH. We see it blocking legilimency. And we see it blocking physical things. I think it's clear that the Shield Charm evolved significantly beyond JKR's original plans for it. - In the event, JKR almost universally relies on "Finite Incantatem" as a spell which undoes more or less everything, with just a few exceptions. This rather undermines there being a system of specific counters for every spell. - JKR confused the terminology by also using the word "counter" to mean offensive magic cast in a defensive way - see Hermione's argument with Umbridge, Bellatrix's "counter spell" which took the head off a statue, and (possibly) Dumbledore giving Harry permission to cast counter-jinxes in HBP. In terms of how I use them: I like the idea that you need to know specific counters rather than being able to rely on the Shield Charm for all magical threats. In enriches defensive magic. However, I also like that powerful wizards are able to cast a powerful general-purpose shield. I feel like the existence of such a spell is important for wizards vs. Muggle reasons. Solution: the default behaviour of the Shield Charm is quite limited - it blocks only minor jinxes, as stated in canon. However, an advanced student of defensive magic can imbue the Shield Charm with additional properties. In particular, if you know a specific counter-jinx/hex/curse, you can cast the Shield Charm in such a way that it is imbued with that counter-spell. Or perhaps if you know the Flame-Freezing Charm, then your shield will be imbued with that property to protect you from fire. So the more you have in your defensive arsenal, the more versatile your shield becomes. I think this compromise preserves both the importance of knowledge of specific defensive magic and the utility of a powerful Shield Charm.