The Teaching
This Principle embodies the truth that "everything is dual"; "everything has two poles"; "everything has its pair of opposites." These old Hermetic axioms explain ancient paradoxes: "opposites are identical in nature, but different in degree"; "the pairs of opposites may be reconciled"; "extremes meet."
Heat and Cold, although "opposites," are really the same thing - the differences consisting merely of degrees of the same thing. Look at your thermometer and see if you can discover where "heat" terminates and "cold" begins!
Mental Polarity
The same Principle operates on the Mental Plane. Take "Love and Hate" - two mental states apparently totally different. Yet there are degrees of Love and degrees of Hate, and a middle point where we use "Like or Dislike," which shade into each other so gradually that sometimes we cannot tell which we feel.
More importantly, it is possible to change the vibrations of Hate to Love, in one's own mind and in the minds of others. "Good and Evil" are but the poles of the same thing, and the Hermetist understands the art of transmuting Evil into Good by application of the Principle of Polarity.
The Art of Polarization
Things belonging to different classes cannot be transmuted into each other, but things of the same class may have their polarity changed. Love never becomes East or Red - but it may turn into Hate, and Hate may be transformed into Love by changing its polarity.
Courage may be transmuted into Fear, and the reverse. By raising mental vibrations along the line of Fear-Courage, a fearful man can be filled with the highest Courage. The "Art of Polarization" becomes a phase of "Mental Alchemy" known and practiced by the ancient and modern Hermetic Masters.