In the following excerpt, author John Michael Greer explains that monsters have something valuable to teach us about ourselves and our world.

A thousand years ago, vampires and shapeshifters, spirits of the ancestors and spirits that were never human at all, intelligent beings with subtle bodies or none, were as much a matter of everyday life then as electricity is now.

But we know better nowadays, of course.

Don't we?

This book is based on the uncomfortable knowledge that we don't know better-that at least some of these entities had, and still have, a reality that goes beyond the limits of human imagination and human psychology. For most people nowadays, such ideas would be terrifying if they weren't so preposterous. Plenty of modern Americans believe that UFOs are spacecraft from other worlds and psychics can bend silverware with their minds-but the existence of vampires and werewolves? To make things worse, this book explores such beings from the standpoint of an equally discredited system of thought: the traditional lore of Western ceremonial magic, which has been denounced and derided by right-thinking folk ever since the end of the Renaissance.

The word "monster" comes from the Latin monstrum, "that which is shown forth or revealed." The same root also appears in the English word "demonstrate," and several less common words (such as "remonstrance") that share the same sense of revealing, disclosing, or displaying. In the original sense of the word, a monster is a revelation, something shown forth.

This may seem worlds away from the usual modern meaning of the word "monster"-a strange, frightening and supposedly mythical creature-but here, as elsewhere in the realm of monsters, appearances deceive. Certainly, monsters are strange, at least to those raised in modern ways of approaching the world. As we'll see, too, monsters have a great deal to do with the realm of myth, although this latter word (like "monster" itself) has older and deeper meanings that evade our modern habits of thought. The association between monsters and terror, too, has practical relevance, even when the creatures we call "monsters" fear us more than we fear them.

The myth, the terror, and the strangeness all have their roots in the nature of the realm of monsters and the monstrous-a world of revelations, where the hidden and the unknown show furtive glimpses of themselves. If we pay attention to them, monsters do have something to reveal. They show us the reality of the impossible, or of those things we label impossible; they point out that the world we think we live in, and the world we actually inhabit, may not be the same place at all.