"I say to you againe, doe not call up Any that you can not put downe"
- H.P. Lovecraft, The Case of Charles Dexter Ward
Extracted from a novella by H.P. Lovecraft the Charles Dexter Ward Principle is a fundamental principle of magic and, indeed, life in general. It's a more eldritch version of not biting off more than you can chew, but particularly appropriate when you are dealing with forces outside the scope of human capability.
The original quote goes on to warn specifically against calling up anything that has the ability to summon in its own right and can then call for allies over which you have no control at all.
Game and Story Use
- Beating this into your players is fun - in Call of Cthulu in particular the players need to learn that you don't cast the contact/summon spell until you know the binding spell to go with it…
- You can pull it off with Demons and Devils in D&D, as well. Many can gate in more of their kind. Usually they gate in weaker types, so if the PCs can deal with the first Demon, they can probably beat any reinforcements. But, if the PCs leave the demon trapped in a magic circle but otherwise unsupervised, there's not telling what mischief those secondary or tertiary demons might get in to.
- If you're crafting your own campaign setting or game system, you can use this as a way to make functional magic seem more dangerous, exciting, and "magical". Make summoning or conjuring easy, but controlling the magic once it's unleashed much harder.
- In such a setting, the difference between a "noob" and a veteran isn't so much power-level as it is finesse and safety. This works great for one-shots, convention games, and short campaigns. It may or may not be as suitable for longer-running campaigns, depending on your player's desires in regards to experience and character advancement.
- Giving the players tons of power and then holding them responsible for the ripples and side effects it unleashes can be lots of fun. Some players take to it poorly, but in my experience most really enjoy the mayhem this causes.