I'm a big fan of Vancian magic. Spells are basically the words of creation, but because they defy logic as soon as you speak them they vacate your logical mind like a dream. This also makes recording them difficult, and passing them down take years of effort, and with every passing decade more and more spells are lost permanently, with the world's wizards well aware of the fact that someday their entire profession will no longer exist.

It gets a bad rap because people think keeping track of spell slots in D&D is annoying, but it's a great way to convey a world where magic is on the decline.