Origins of Magic

DM's Note: this is not set in stone, nor is it meant to be all-encompassing. If you have a different idea on how your PC has obtained their magic, then I am open to hear your pitch.

Magic among the Planes
Each of the planes radiates its own unique pattern of energy out into the Astral Expanse. As these energies join together out in the expanse, they mix and mingle to form a current of power than ebbs and flow through and around each plane. This stream of energy is the well of power that magic is drawn from. Some study ways to control the energy and make it do what they desire, while others can guide the natural flow of one or more of the different types of energy within the stream to produce spectacular magic.

Artificer:
Through your pursuit of creation you have learned how to harness and mold the elemental forces of the planes. Your abilities are a result of trial and error experimentation. The ability to cast higher levels of magic are usually an indicator of a great commitment to the craft, and a sharp intellect.

Barbarian:
Whatever magic you wield is not through study or experimentation, it is through your will and connection to the wilds of the plane. Living a rugged and natural life has deepened your bon with the plane, and by extension the natural flow of magic, giving you the ability to evoke some of its power either intentionally or not.

Bard:
A bard is constantly performing for the gods. If they perform well and entertain the deities that watch, they gain their favors and can cast their magic.

Cleric:
Devotion to a being of great power, a cleric is a chosen of that deity. To keep their powers they are expected act in accordance with the tenets of the being. While in the favor of their deity they wield potent magic, with higher levels of magic indicating experience and adherence to the ways of their deity.

Druid:
Becoming one with the land, a druid's essence harmonizes with the flow of natural magic permeating the area. They use this harmony to alter and guide the flow of magic to create the spell they desire

Fighter
Training if you so choose to dabble in magic, usually the same way a wizard learns.

Monk
A monk as honed their ability to use the trace amounts of magic that everything slowly emits. To monks it is known as Ki, they use this Ki to produce paranormal effects within themselves and within others.

Paladin
The first half of the path to becoming a paladin is to swear a binding oath, committing themselves to a set of rules that they will follow until their oath is fulfilled, many of these oaths are for life. The second half of the path is for a Deity to hear your oath and decide to back you on it, deeming your oath worthy and granting you the power needed to fulfill it. casting at higher levels usually shows you adherence and commitment to your oath.

Ranger
Much like druid and barbarian, you proximity to undisturbed natural magic makes it easier for you to access it and draw upon it. A deity manybe assisting you in you spell casting, or it could just be your intimate connection with nature.

Rogue
Training if you so choose to dabble in magic, usually the same way a wizard learns.

Sorcerer
Born with an innate connection to at least one of the main sources of magic. Casting comes as easy as breathing, and you can feel and manipulate the magic within you quite easily.

Warlock
You made a deal with something that could give you power. They have basically total control over said power, and use that as leverage if you act against their wishes.

Wizard
Through years of study you have learned how you bend the magic of the land to your will. Arcane casting acknowledges the limitations of doing things the natural way, and throws those limits out the window. With enough time and study a Wizard can achieve almost any magical outcome they desire.