[Galadriel55]

I think that the magic that the istari, the nazgul, the elves, and whatever other creatures do is really their willpower. The incantations are like a way to turn it into whatever action you want to happen. One of the easiest things to explain is how the Dunadains, Gimli, and Legolas were able to cross Gondor with hardly any rest. It is supernatural for anyone to be so...strong, full of energy, etc. I think that what happened is that Aragorn, who had great inner power, enabled himself and his army to ake this journey.
This also explains why someone like Pippin wouldn't be able to make something with an incantation - he has inner strength, but lacks the inner power.
Elven magic is very often connected to nature, just like elves. I guess that since they live for so long, they establish connections with their environment, and nature helps them (for example: Bruinen swept the Nazguls away; Galadriel's mirror was water that a star shone upon, etc).
Even today there are peo0ple who can do things with their thought, read minds, and that sort of stuff.