All Wizards Are Warlocks

No human can just learn to manipulate magic.

The so-called wizards who brag and drone on about their long years of careful study that granted them supernatural powers simply don't want to acknowledge the obvious: You cannot build a tower without the foundations. You cannot make a cow fly without some serious help. Indeed, humans can use magic - but only with help, if they are given the Gift by a spirit of some sort.

A patron, if you will.

Thus every magic user must follow a certain pact that grants them access to their preternatural powers, though the exact nature of such pact and the price they pay differs wildly between practitioners. While there are no hard and fast rules for sorting magicians into neat and clear-cut categories, at least some of the most common kinds of magic users and their approaches to magic and the spirit world are discussed below.
 

"Wait! I can go up to ten babies, but not a single one more."

 
Sorcerers would be the exception that proves the rule, as they do have an inherent gift of magic that they can train and hone on their own - except they are not human, not fully. Their pact is one of blood and bloodline, their patron the non-human ancestor who set their whole family apart from the rest of the human race.

Sorcery tends to have a very narrow focus - a dragon may sire a lineage of pyromancers, a fairy a line of illusionists - and departing from one's hereditary, traditional craft is basically impossible. Indeed, sorcerous families oftentimes gravitate towards a strong sense of tradition, elitism and purity of blood, stoked by the fear of loosing that which makes them special. As their bloodline gets diluted over generations, the sorcerous spark grows ever weaker and their gift of magic eventually fades away. This unfortunately drives many sorcerers to search for ways of preserving the power of their family. Affairs with non-humans and incestuous relationships are regrettably common among sorcerers. And while this does keep the magic in the family, it also sets the sorcerers ever further apart from true humanity, with each new inbred generation being more powerful, more mutated and more insane, until at one point, it's no longer possible to consider them human magicians any more, but rather magic beings in their own right.

Such creatures are then quite likely to find a human spouse for themselves, and the cycle starts anew.

Mediums pay for magic with their bodies. In exchange for power, they offer agency to any spirit who desires a more physical presence in Reality. In short, they willingly let themselves be possessed.

This form of the Craft is probably the easiest to start with - a spirit who would enjoy a ride in a living body can be found pretty much everywhere and all a prospective medium has to do is keep an open mind as say "Yes" - but doing it in a safe and useful manner is very hard. After all, you are opening your Self to a magical being and the only way to gain more power is to let more powerful spirits in. As the saying goes, there are no bad mediums, only dead mediums.

The good ones, though, eventually end up either bonding with a single spirit and gaining a great, focused power through the breadth and depth of their connection; or amassing a host of multiple spirits for short-term possessions, each a different tool in their toolbox. The former run a high risk of eventually merging with their possessing spirit and shedding their humanity as a newborn magical beast. The latter should take care to play all of their spirits off against each other, lest the spirits grow discontent with their limited access to the medium's body and unite their forces, resulting in an involuntary possession by the whole host of spirits, banishment of the medium's soul and the birth of a creature known as the wisp-lord.

Priests are quite obviously serving a higher power, a distant deity that deigns to answer some of their pleas for help in exchange for regular prayers and rites. Never forget, though, that there's really not that much of a difference between a cleric of the Lord of Light and a cultist of He-Who-Lurks-In-Corners - both are trying to catch the attention of a being that could squash a city without even meaning to, and that doesn't really listen to, care about or understand its worshippers. Priestly magic is very powerful, but unreliable and prone to missing the point or being helpful only in mysterious, alien ways.

Evangelists are often seen as priests with another name, but that's plain wrong. Evangelists don't work with the gods, they work with angels. And where priests might be fine with going through the motions of reverence with no true faith or zeal behind it - they are so deep beneath the notice of their patrons that all but the most egregious sins and mistakes are overlooked - evangelists have to always stay true in their ardour.

Indeed, angels tend to take a great interest in evangelists, keeping them an unseen company at all times, helping and guarding them, but never forgiving. Angels are spirits of holy war and vengeance. Angels are razor focused on battling evil in all forms and shapes, enabling a lone evangelist to repel an army of the dead or go toe to toe with a greater demon, until they misstep and get smote on the spot.

Diabolists are the archetypal warlocks. They made a pact for power or knowledge, pledging their services or selling some bits and bobs of themselves to a patron who has need of what the warlock offers and can provide magic in exchange. The name "diabolist" is misleading, as they didn't necessarily have to make a deal with the devil - they could have made a deal with any number of other otherworldly entities - yet the principal difference from other magicians is that a diabolist's power is strictly contractual, its limits and conditions clearly stipulated. The magic of diabolists is the most reliable of all the forms of practice, as long as they are able and willing to keep their side of the bargain.

Druids cater either to the many small nature spirits that infuse every tree and spring and herd of animals, or to the great spirits of nature who oversee whole forests, mountains or islands. They build up favour with a location until the very wind and ground and undergrowth likes them and tries to help them and fulfil their every wish. They hold great sway while in their place of power, but they are also greatly limited should they leave. While the spiritual word of mouth may allow them to draw upon some of the favour they amassed even elsewhere, the spirits of nature are jealous, fickle and territorial - if the druid is gone for too long from their demesne, they may return to find that the place has forgotten them, or even worse, faults them for leaving.

Shamans work with lesser spirits too, but where druids build their relationship with all spirits in a location, shamans try to win the affections of specific spirits - ancestral and heroic ghosts, petty gods, minor demons or Folk, anything goes. All their magic is very much quid pro quo, and the nature of favours they may draw upon depends on the kind of spirits they commune with. They are the socialites of magic users, they have connections, they know a guy who knows a guy. They also have to juggle their spirit friendships very carefully, as trying to woo two feuding spirits could result in some bad blood very easily and getting bad-mouthed by an angry spirit might seriously threaten their Craft.

Elementalists, necromancers and demonologists are all proud to differentiate themselves from one another, but they are all in fact just specialized summoners. They are not even that different from shamans, except that a shaman has a long-standing relationship with their spirits, whereas a (whichever) summoner calls upon any random spirit of their chosen type, offering it a payment for one specific task. Take it or leave it, we don't need to see each other again once the job is done.

An elementalist doesn't throw a fireball, she feeds some delicious bat guano to a fire elemental and it makes an explosion for her. A necromancer doesn't animate the dead, he offers to return corporeality back to the dead in exchange for servitude. And a demonologist exchanges souls for services.

Magi are sometimes disparagingly called the dabblers or wandslingers, or with less prejudice the collectors. They didn't make a pact or build up favour - they found a stick and learned how to activate it.

Of course, that is an exaggeration. A magus is often a determined individual who sacrificed a lot to win their wand or spell-blade or another artifact. Their magic is simple and strong and stable, but also set in stone - there is no flexibility, no growth. Once they learn to use their artifact, that's all they will ever be able to do unless they hunt down another artifact. Plus they are the only type of magician whose magic can easily be stolen. Easy come, easy go, as they say.

Alchemists are the strangest bunch - they force magic to happen. Other magicians occasionally fabricate magic items, but alchemists specialize in it. They create spirit-lures in the form of tasty potions, interesting scribblings on scrolls, or strange alloys of metals forged into rings; then they bind the spirits they entice, with the only way out of the binding being to perform as requested. They can trap nearly any magical being and when they negotiate, it's always from the position of power. They are masters of magic runes and circles and sigils. They build golems, craft enchanted arms and armour, even transmogrify living creatures with biomantic surgery-seals. With the right formula, they can make nearly any magic happen. The greatest of them take years to reshape the landscape into geomantic bindings that enslave gods.

They are also universally hated by the spirits. They have to be very meticulous and methodical, because if they make the tiniest mistake, all hell breaks loose.

Goblin kings, or filthomancers, are the living proof that even awful things can be useful. It is a common knowledge that goblinism is contagious. It is not a normal disease, though, but rather a spiritual one. A wild disease-spirit that can nonetheless be tamed with gifts and drawn on for magic.

Everything a goblin can do, a goblin king can do better - creating a variety of noxious and toxic odours, slipping anywhere unnoticed, smelling out everything from what you had for lunch to hidden treasure or emotions, surviving nearly anything by becoming more disfigured and disgusting, getting bigger and stronger and tougher by eating a lot, making others suffer. And with the favour of the goblin-spirit, the "friendship" of goblins comes hand in hand. A prospective goblin queen will soon find herself with a cohort of goblins that follow her everywhere (especially where she doesn't want them to follow) and kind-of help with everything (but mainly make a big mess) - thus also the title of a queen or king.

Importantly though, goblin kings are prime carriers of goblinism. Everything they touch and anyone they interact with will be at least a little bit tainted - a little bit under their control. They don't need to build a trapped mansion for themselves - any building they live in will eventually become an ugly, filthy goblin-shack, full of nasty and dangerous surprises for trespassers. They have no need for magic weapons - any knife they use for a while will become a serrated, rusty, poisonous, deadly goblin-shank. If you're willing to debase yourself enough, goblin magic can be disgustingly useful and treacherously versatile.
 

For the low price of your sanity...
From Magic the Gathering

 
And what about the wizards? Those who would be bloody insulted if you called them a warlock, insulted enough to singe your eyebrows off with a lightning bolt, even? Those who are always accompanied by their familiar, a spiritual guide and helper and friend? A familiar that they made a pact with, a pact for power or knowledge?

Yeah...