William Butler Yeats on Magic (from Essays and Introductions):

I believe in the practice and philosophy of what we have agreed to call magic, in what I must call the evocation of spirits, though I do not know what they are, in the power of creating magical illusion, in the visions of truth in the depths of the mind when the eyes are closed; and I believe in three doctrines, which have, as I think, been handed down from early times and been the foundation of nearly all magical practices. These doctrines are:

(1) That the borders of our minds are ever-shifting, and that many minds can flow into one another, as it were, and create or reveal a single mind, a single energy.

(2) That the borders of our memories are as shifting, and that our memories are a part of one great memory, the memory of Nature herself.

(3) That this great mind and great memory can be evoked by symbols.